[PATCH v5 0/8] support for bitmap (and hence CPU) list "N" abbreviation

[PATCH v5 0/8] support for bitmap (and hence CPU) list "N" abbreviation

[Paul Gortmaker]

This is the 5th and final version of this series.  We got some good
improvements, like adding self-tests, using "N" as "just another number"
that could be used anywhere, and making things not CPU specific.

But now it is time to close this review out since is down to just
hand-wringing over hypothetical use cases, bikeshedding on upper/lower
case, and a wild goose chase on trying to avoid adding a function arg.

So, once again - thanks to all who provided input; it was all considered
even if not all of it was used.  And in that vein, just to be clear:

1) There will be no adaptive modifying or guessing what the user meant if
a range turns out to be invalid.  The caller will be responsible for
handling the -EINVAL just as things are currently today.

2) There will be no use of "L" or lower case "n" because there is simply
no need for it.  Yes, it would be simple enough to add, but it complicates
things and would also be impossible to remove later, once it went mainline.


The original text from v4 follows:

The basic objective here was to add support for "nohz_full=8-N" and/or
"rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference
to the last core, evaluated at boot for anything using a CPU list.

The thinking behind this, is that people carve off a few early CPUs to
support housekeeping tasks, and perhaps dedicate one to a busy I/O
peripheral, and then the remaining pool of CPUs out to the end are a
part of a commonly configured pool used for the real work the user
cares about.

Extend that logic out to a fleet of machines - some new, and some
nearing EOL, and you've probably got a wide range of core counts to
contend with - even though the early number of cores dedicated to the
system overhead probably doesn't vary.

This change would enable sysadmins to have a common bootarg across all
such systems, and would also avoid any off-by-one fencepost errors that
happen for users who might briefly forget that core counts start at zero.

Originally I did this at the CPU subsys level, but Yury suggested it
be moved down further to bitmap level itself, which made the core 
implementation smaller and less complex, but the series longer.

New self tests are added to better exercise what bitmap range/region
currently supports, and new tests are added for the new "N" support.

Also tested boot arg and the post-boot cgroup use case as per below:

   root@hackbox:~# cat /proc/cmdline 
   BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2
   root@hackbox:~# dmesg|grep Offl
   rcu:     Offload RCU callbacks from CPUs: 2-3,8,10,12,14.

   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   
   root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus
   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   10-15
   root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus
   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   15

This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file.

Note that "N" is a dynamic quantity, and can change scope if the bitmap
is changed in size.  So at the risk of stating the obvious, don't use it
for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff.

Paul.
---

[v5: go back to v3 location of "nbits" in region.  Add acks/reviewed.]

[v4: pair nbits with region, instead of inside it.  Split EINVAL and
 ERANGE tests.  Don't handle start/end/offset within a macro to
 abstract away nbits usage.  Added some Reviwed-by/Ack tags.]
 https://lore.kernel.org/lkml/20210209225907.78405-1-paul.gortmaker@windriver.com/

[v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs.
 just being allowed at end of range like "0-N".  Add new self-tests.  Drop
 "all" and "none" aliases as redundant and not worth the extra complication. ]
 https://lore.kernel.org/lkml/20210126171141.122639-1-paul.gortmaker@windriver.com/

[v2: push code down from cpu subsys to core bitmap code as per
 Yury's comments.  Change "last" to simply be "N" as per PeterZ.]
 https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/

[v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/

Cc: Li Zefan <lizefan@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>



Paul Gortmaker (8):
  lib: test_bitmap: clearly separate ERANGE from EINVAL tests.
  lib: test_bitmap: add tests to trigger ERANGE case.
  lib: test_bitmap: add more start-end:offset/len tests
  lib: bitmap: fold nbits into region struct
  lib: bitmap: move ERANGE check from set_region to check_region
  lib: bitmap: support "N" as an alias for size of bitmap
  lib: test_bitmap: add tests for "N" alias
  rcu: deprecate "all" option to rcu_nocbs=

 .../admin-guide/kernel-parameters.rst         |  7 +++
 .../admin-guide/kernel-parameters.txt         |  4 +-
 kernel/rcu/tree_plugin.h                      |  6 +--
 lib/bitmap.c                                  | 49 +++++++++++--------
 lib/test_bitmap.c                             | 46 ++++++++++++++---
 5 files changed, 79 insertions(+), 33 deletions(-)

-- 
2.30.0

[PATCH 1/8] lib: test_bitmap: clearly separate ERANGE from EINVAL tests.

[Paul Gortmaker]

This block of tests was meant to find/flag incorrect use of the ":"
and "/" separators (syntax errors) and invalid (zero) group len.

However they were specified with an 8 bit width and 32 bit operations,
so they really contained two errors (EINVAL and ERANGE).

Promote them to 32 bit so it is clear what they are meant to target.
Then we can add tests specific for ERANGE (no syntax errors, just
doing 32bit op on 8 bit width, plus a typical 9-on-8 fencepost error).

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 lib/test_bitmap.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 4425a1dd4ef1..589f2a34ceba 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -338,12 +338,12 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = {
 	{-EINVAL, "-1",	NULL, 8, 0},
 	{-EINVAL, "-0",	NULL, 8, 0},
 	{-EINVAL, "10-1", NULL, 8, 0},
-	{-EINVAL, "0-31:", NULL, 8, 0},
-	{-EINVAL, "0-31:0", NULL, 8, 0},
-	{-EINVAL, "0-31:0/", NULL, 8, 0},
-	{-EINVAL, "0-31:0/0", NULL, 8, 0},
-	{-EINVAL, "0-31:1/0", NULL, 8, 0},
-	{-EINVAL, "0-31:10/1", NULL, 8, 0},
+	{-EINVAL, "0-31:", NULL, 32, 0},
+	{-EINVAL, "0-31:0", NULL, 32, 0},
+	{-EINVAL, "0-31:0/", NULL, 32, 0},
+	{-EINVAL, "0-31:0/0", NULL, 32, 0},
+	{-EINVAL, "0-31:1/0", NULL, 32, 0},
+	{-EINVAL, "0-31:10/1", NULL, 32, 0},
 	{-EOVERFLOW, "0-98765432123456789:10/1", NULL, 8, 0},
 
 	{-EINVAL, "a-31", NULL, 8, 0},
-- 
2.30.0

[PATCH 2/8] lib: test_bitmap: add tests to trigger ERANGE case.

[Paul Gortmaker]

Add tests that specify a valid range, but one that is outside the
width of the bitmap for which it is to be applied to.  These should
trigger an -ERANGE response from the code.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 lib/test_bitmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 589f2a34ceba..172ffbfa83c4 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -338,6 +338,8 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = {
 	{-EINVAL, "-1",	NULL, 8, 0},
 	{-EINVAL, "-0",	NULL, 8, 0},
 	{-EINVAL, "10-1", NULL, 8, 0},
+	{-ERANGE, "8-8", NULL, 8, 0},
+	{-ERANGE, "0-31", NULL, 8, 0},
 	{-EINVAL, "0-31:", NULL, 32, 0},
 	{-EINVAL, "0-31:0", NULL, 32, 0},
 	{-EINVAL, "0-31:0/", NULL, 32, 0},
-- 
2.30.0

[PATCH 3/8] lib: test_bitmap: add more start-end:offset/len tests

[Paul Gortmaker]

There are inputs to bitmap_parselist() that would probably never
be entered manually by a person, but might result from some kind of
automated input generator.  Things like ranges of length 1, or group
lengths longer than nbits, overlaps, or offsets of zero.

Adding these tests serve two purposes:

1) document what might seem odd but nonetheless valid input.

2) don't regress from what we currently accept as valid.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 lib/test_bitmap.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 172ffbfa83c4..9c6a88c480c1 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -35,6 +35,8 @@ static const unsigned long exp1[] __initconst = {
 	BITMAP_FROM_U64(0x3333333311111111ULL),
 	BITMAP_FROM_U64(0xffffffff77777777ULL),
 	BITMAP_FROM_U64(0),
+	BITMAP_FROM_U64(0x00008000),
+	BITMAP_FROM_U64(0x80000000),
 };
 
 static const unsigned long exp2[] __initconst = {
@@ -335,6 +337,26 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = {
 	{0, " ,  ,,  , ,   ",		&exp1[12 * step], 8, 0},
 	{0, " ,  ,,  , ,   \n",		&exp1[12 * step], 8, 0},
 
+	{0, "0-0",			&exp1[0], 32, 0},
+	{0, "1-1",			&exp1[1 * step], 32, 0},
+	{0, "15-15",			&exp1[13 * step], 32, 0},
+	{0, "31-31",			&exp1[14 * step], 32, 0},
+
+	{0, "0-0:0/1",			&exp1[12 * step], 32, 0},
+	{0, "0-0:1/1",			&exp1[0], 32, 0},
+	{0, "0-0:1/31",			&exp1[0], 32, 0},
+	{0, "0-0:31/31",		&exp1[0], 32, 0},
+	{0, "1-1:1/1",			&exp1[1 * step], 32, 0},
+	{0, "0-15:16/31",		&exp1[2 * step], 32, 0},
+	{0, "15-15:1/2",		&exp1[13 * step], 32, 0},
+	{0, "15-15:31/31",		&exp1[13 * step], 32, 0},
+	{0, "15-31:1/31",		&exp1[13 * step], 32, 0},
+	{0, "16-31:16/31",		&exp1[3 * step], 32, 0},
+	{0, "31-31:31/31",		&exp1[14 * step], 32, 0},
+
+	{0, "0-31:1/3,1-31:1/3,2-31:1/3",	&exp1[8 * step], 32, 0},
+	{0, "1-10:8/12,8-31:24/29,0-31:0/3",	&exp1[9 * step], 32, 0},
+
 	{-EINVAL, "-1",	NULL, 8, 0},
 	{-EINVAL, "-0",	NULL, 8, 0},
 	{-EINVAL, "10-1", NULL, 8, 0},
-- 
2.30.0

[PATCH 4/8] lib: bitmap: fold nbits into region struct

[Paul Gortmaker]

This will reduce parameter passing and enable using nbits as part
of future dynamic region parameter parsing.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 lib/bitmap.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 75006c4036e9..162e2850c622 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -487,24 +487,24 @@ EXPORT_SYMBOL(bitmap_print_to_pagebuf);
 
 /*
  * Region 9-38:4/10 describes the following bitmap structure:
- * 0	   9  12    18			38
- * .........****......****......****......
- *	    ^  ^     ^			 ^
- *      start  off   group_len	       end
+ * 0	   9  12    18			38	     N
+ * .........****......****......****..................
+ *	    ^  ^     ^			 ^	     ^
+ *      start  off   group_len	       end	 nbits
  */
 struct region {
 	unsigned int start;
 	unsigned int off;
 	unsigned int group_len;
 	unsigned int end;
+	unsigned int nbits;
 };
 
-static int bitmap_set_region(const struct region *r,
-				unsigned long *bitmap, int nbits)
+static int bitmap_set_region(const struct region *r, unsigned long *bitmap)
 {
 	unsigned int start;
 
-	if (r->end >= nbits)
+	if (r->end >= r->nbits)
 		return -ERANGE;
 
 	for (start = r->start; start <= r->end; start += r->group_len)
@@ -640,7 +640,8 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
 	struct region r;
 	long ret;
 
-	bitmap_zero(maskp, nmaskbits);
+	r.nbits = nmaskbits;
+	bitmap_zero(maskp, r.nbits);
 
 	while (buf) {
 		buf = bitmap_find_region(buf);
@@ -655,7 +656,7 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
 		if (ret)
 			return ret;
 
-		ret = bitmap_set_region(&r, maskp, nmaskbits);
+		ret = bitmap_set_region(&r, maskp);
 		if (ret)
 			return ret;
 	}
-- 
2.30.0

[PATCH 5/8] lib: bitmap: move ERANGE check from set_region to check_region

[Paul Gortmaker]

It makes sense to do all the checks in check_region() and not 1/2
in check_region and 1/2 in set_region.

Since set_region is called immediately after check_region, the net
effect on runtime is zero, but it gets rid of an if (...) return...

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 lib/bitmap.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 162e2850c622..833f152a2c43 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -500,17 +500,12 @@ struct region {
 	unsigned int nbits;
 };
 
-static int bitmap_set_region(const struct region *r, unsigned long *bitmap)
+static void bitmap_set_region(const struct region *r, unsigned long *bitmap)
 {
 	unsigned int start;
 
-	if (r->end >= r->nbits)
-		return -ERANGE;
-
 	for (start = r->start; start <= r->end; start += r->group_len)
 		bitmap_set(bitmap, start, min(r->end - start + 1, r->off));
-
-	return 0;
 }
 
 static int bitmap_check_region(const struct region *r)
@@ -518,6 +513,9 @@ static int bitmap_check_region(const struct region *r)
 	if (r->start > r->end || r->group_len == 0 || r->off > r->group_len)
 		return -EINVAL;
 
+	if (r->end >= r->nbits)
+		return -ERANGE;
+
 	return 0;
 }
 
@@ -656,9 +654,7 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
 		if (ret)
 			return ret;
 
-		ret = bitmap_set_region(&r, maskp);
-		if (ret)
-			return ret;
+		bitmap_set_region(&r, maskp);
 	}
 
 	return 0;
-- 
2.30.0

[PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Paul Gortmaker]

While this is done for all bitmaps, the original use case in mind was
for CPU masks and cpulist_parse() as described below.

It seems that a common configuration is to use the 1st couple cores for
housekeeping tasks.  This tends to leave the remaining ones to form a
pool of similarly configured cores to take on the real workload of
interest to the user.

So on machine A - with 32 cores, it could be 0-3 for "system" and then
4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
setting up the worker pool of CPUs.

But then newer machine B is added, and it has 48 cores, and so while
the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.

Multiple deployment becomes easier when we can just simply replace 31
and 47 with "N" and let the system substitute in the actual number at
boot; a number that it knows better than we do.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Yury Norov <yury.norov@gmail.com> # move it from CPU code
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 .../admin-guide/kernel-parameters.rst         |  7 ++++++
 lib/bitmap.c                                  | 22 ++++++++++++++-----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index 682ab28b5c94..7733a773f5f8 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -68,6 +68,13 @@ For example one can add to the command line following parameter:
 
 where the final item represents CPUs 100,101,125,126,150,151,...
 
+The value "N" can be used to represent the numerically last CPU on the system,
+i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
+
+Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
+to change, such as less cores in the CPU list, then N and any ranges using N
+will also change.  Use the same on a small 4 core system, and "16-N" becomes
+"16-3" and now the same boot input will be flagged as invalid (start > end).
 
 
 This document may not be entirely up to date and comprehensive. The command
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 833f152a2c43..9f4626a4c95f 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -519,11 +519,17 @@ static int bitmap_check_region(const struct region *r)
 	return 0;
 }
 
-static const char *bitmap_getnum(const char *str, unsigned int *num)
+static const char *bitmap_getnum(const char *str, unsigned int *num,
+				 unsigned int lastbit)
 {
 	unsigned long long n;
 	unsigned int len;
 
+	if (str[0] == 'N') {
+		*num = lastbit;
+		return str + 1;
+	}
+
 	len = _parse_integer(str, 10, &n);
 	if (!len)
 		return ERR_PTR(-EINVAL);
@@ -571,7 +577,9 @@ static const char *bitmap_find_region_reverse(const char *start, const char *end
 
 static const char *bitmap_parse_region(const char *str, struct region *r)
 {
-	str = bitmap_getnum(str, &r->start);
+	unsigned int lastbit = r->nbits - 1;
+
+	str = bitmap_getnum(str, &r->start, lastbit);
 	if (IS_ERR(str))
 		return str;
 
@@ -581,7 +589,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
 	if (*str != '-')
 		return ERR_PTR(-EINVAL);
 
-	str = bitmap_getnum(str + 1, &r->end);
+	str = bitmap_getnum(str + 1, &r->end, lastbit);
 	if (IS_ERR(str))
 		return str;
 
@@ -591,14 +599,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
 	if (*str != ':')
 		return ERR_PTR(-EINVAL);
 
-	str = bitmap_getnum(str + 1, &r->off);
+	str = bitmap_getnum(str + 1, &r->off, lastbit);
 	if (IS_ERR(str))
 		return str;
 
 	if (*str != '/')
 		return ERR_PTR(-EINVAL);
 
-	return bitmap_getnum(str + 1, &r->group_len);
+	return bitmap_getnum(str + 1, &r->group_len, lastbit);
 
 no_end:
 	r->end = r->start;
@@ -625,6 +633,10 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
  * From each group will be used only defined amount of bits.
  * Syntax: range:used_size/group_size
  * Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769
+ * The value 'N' can be used as a dynamically substituted token for the
+ * maximum allowed value; i.e (nmaskbits - 1).  Keep in mind that it is
+ * dynamic, so if system changes cause the bitmap width to change, such
+ * as more cores in a CPU list, then any ranges using N will also change.
  *
  * Returns: 0 on success, -errno on invalid input strings. Error values:
  *
-- 
2.30.0

[PATCH 7/8] lib: test_bitmap: add tests for "N" alias

[Paul Gortmaker]

These are copies of existing tests, with just 31 --> N.  This ensures
the recently added "N" alias transparently works in any normally
numeric fields of a region specification.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 lib/test_bitmap.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 9c6a88c480c1..a6048278d027 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -354,6 +354,16 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = {
 	{0, "16-31:16/31",		&exp1[3 * step], 32, 0},
 	{0, "31-31:31/31",		&exp1[14 * step], 32, 0},
 
+	{0, "N-N",			&exp1[14 * step], 32, 0},
+	{0, "0-0:1/N",			&exp1[0], 32, 0},
+	{0, "0-0:N/N",			&exp1[0], 32, 0},
+	{0, "0-15:16/N",		&exp1[2 * step], 32, 0},
+	{0, "15-15:N/N",		&exp1[13 * step], 32, 0},
+	{0, "15-N:1/N",			&exp1[13 * step], 32, 0},
+	{0, "16-N:16/N",		&exp1[3 * step], 32, 0},
+	{0, "N-N:N/N",			&exp1[14 * step], 32, 0},
+
+	{0, "0-N:1/3,1-N:1/3,2-N:1/3",		&exp1[8 * step], 32, 0},
 	{0, "0-31:1/3,1-31:1/3,2-31:1/3",	&exp1[8 * step], 32, 0},
 	{0, "1-10:8/12,8-31:24/29,0-31:0/3",	&exp1[9 * step], 32, 0},
 
-- 
2.30.0

[PATCH 8/8] rcu: deprecate "all" option to rcu_nocbs=

[Paul Gortmaker]

With the core bitmap support now accepting "N" as a placeholder for
the end of the bitmap, "all" can be represented as "0-N" and has the
advantage of not being specific to RCU (or any other subsystem).

So deprecate the use of "all" by removing documentation references
to it.  The support itself needs to remain for now, since we don't
know how many people out there are using it currently, but since it
is in an __init area anyway, it isn't worth losing sleep over.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 +---
 kernel/rcu/tree_plugin.h                        | 6 ++----
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a10b545c2070..a116c0ff0a91 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4037,9 +4037,7 @@
 				see CONFIG_RAS_CEC help text.
 
 	rcu_nocbs=	[KNL]
-			The argument is a cpu list, as described above,
-			except that the string "all" can be used to
-			specify every CPU on the system.
+			The argument is a cpu list, as described above.
 
 			In kernels built with CONFIG_RCU_NOCB_CPU=y, set
 			the specified list of CPUs to be no-callback CPUs.
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 7e291ce0a1d6..56788dfde922 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1463,14 +1463,12 @@ static void rcu_cleanup_after_idle(void)
 
 /*
  * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
- * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
- * comma-separated list of CPUs and/or CPU ranges.  If an invalid list is
- * given, a warning is emitted and all CPUs are offloaded.
+ * If the list is invalid, a warning is emitted and all CPUs are offloaded.
  */
 static int __init rcu_nocb_setup(char *str)
 {
 	alloc_bootmem_cpumask_var(&rcu_nocb_mask);
-	if (!strcasecmp(str, "all"))
+	if (!strcasecmp(str, "all"))		/* legacy: use "0-N" instead */
 		cpumask_setall(rcu_nocb_mask);
 	else
 		if (cpulist_parse(str, rcu_nocb_mask)) {
-- 
2.30.0

Re: [PATCH v5 0/8] support for bitmap (and hence CPU) list "N" abbreviation

[Paul E. McKenney]

On Sun, Feb 21, 2021 at 03:08:19AM -0500, Paul Gortmaker wrote:
> This is the 5th and final version of this series.  We got some good
> improvements, like adding self-tests, using "N" as "just another number"
> that could be used anywhere, and making things not CPU specific.
> 
> But now it is time to close this review out since is down to just
> hand-wringing over hypothetical use cases, bikeshedding on upper/lower
> case, and a wild goose chase on trying to avoid adding a function arg.
> 
> So, once again - thanks to all who provided input; it was all considered
> even if not all of it was used.  And in that vein, just to be clear:
> 
> 1) There will be no adaptive modifying or guessing what the user meant if
> a range turns out to be invalid.  The caller will be responsible for
> handling the -EINVAL just as things are currently today.
> 
> 2) There will be no use of "L" or lower case "n" because there is simply
> no need for it.  Yes, it would be simple enough to add, but it complicates
> things and would also be impossible to remove later, once it went mainline.

Queued and pushed, thank you!!!

							Thanx, Paul

> The original text from v4 follows:
> 
> The basic objective here was to add support for "nohz_full=8-N" and/or
> "rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference
> to the last core, evaluated at boot for anything using a CPU list.
> 
> The thinking behind this, is that people carve off a few early CPUs to
> support housekeeping tasks, and perhaps dedicate one to a busy I/O
> peripheral, and then the remaining pool of CPUs out to the end are a
> part of a commonly configured pool used for the real work the user
> cares about.
> 
> Extend that logic out to a fleet of machines - some new, and some
> nearing EOL, and you've probably got a wide range of core counts to
> contend with - even though the early number of cores dedicated to the
> system overhead probably doesn't vary.
> 
> This change would enable sysadmins to have a common bootarg across all
> such systems, and would also avoid any off-by-one fencepost errors that
> happen for users who might briefly forget that core counts start at zero.
> 
> Originally I did this at the CPU subsys level, but Yury suggested it
> be moved down further to bitmap level itself, which made the core 
> implementation smaller and less complex, but the series longer.
> 
> New self tests are added to better exercise what bitmap range/region
> currently supports, and new tests are added for the new "N" support.
> 
> Also tested boot arg and the post-boot cgroup use case as per below:
> 
>    root@hackbox:~# cat /proc/cmdline 
>    BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2
>    root@hackbox:~# dmesg|grep Offl
>    rcu:     Offload RCU callbacks from CPUs: 2-3,8,10,12,14.
> 
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
>    
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
>    10-15
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
>    15
> 
> This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file.
> 
> Note that "N" is a dynamic quantity, and can change scope if the bitmap
> is changed in size.  So at the risk of stating the obvious, don't use it
> for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff.
> 
> Paul.
> ---
> 
> [v5: go back to v3 location of "nbits" in region.  Add acks/reviewed.]
> 
> [v4: pair nbits with region, instead of inside it.  Split EINVAL and
>  ERANGE tests.  Don't handle start/end/offset within a macro to
>  abstract away nbits usage.  Added some Reviwed-by/Ack tags.]
>  https://lore.kernel.org/lkml/20210209225907.78405-1-paul.gortmaker@windriver.com/
> 
> [v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs.
>  just being allowed at end of range like "0-N".  Add new self-tests.  Drop
>  "all" and "none" aliases as redundant and not worth the extra complication. ]
>  https://lore.kernel.org/lkml/20210126171141.122639-1-paul.gortmaker@windriver.com/
> 
> [v2: push code down from cpu subsys to core bitmap code as per
>  Yury's comments.  Change "last" to simply be "N" as per PeterZ.]
>  https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/
> 
> [v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/
> 
> Cc: Li Zefan <lizefan@huawei.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> 
> 
> 
> Paul Gortmaker (8):
>   lib: test_bitmap: clearly separate ERANGE from EINVAL tests.
>   lib: test_bitmap: add tests to trigger ERANGE case.
>   lib: test_bitmap: add more start-end:offset/len tests
>   lib: bitmap: fold nbits into region struct
>   lib: bitmap: move ERANGE check from set_region to check_region
>   lib: bitmap: support "N" as an alias for size of bitmap
>   lib: test_bitmap: add tests for "N" alias
>   rcu: deprecate "all" option to rcu_nocbs=
> 
>  .../admin-guide/kernel-parameters.rst         |  7 +++
>  .../admin-guide/kernel-parameters.txt         |  4 +-
>  kernel/rcu/tree_plugin.h                      |  6 +--
>  lib/bitmap.c                                  | 49 +++++++++++--------
>  lib/test_bitmap.c                             | 46 ++++++++++++++---
>  5 files changed, 79 insertions(+), 33 deletions(-)
> 
> -- 
> 2.30.0
> 

Re: [PATCH v5 0/8] support for bitmap (and hence CPU) list "N" abbreviation

[Yury Norov]

On Sun, Feb 21, 2021 at 03:08:19AM -0500, Paul Gortmaker wrote:
> This is the 5th and final version of this series.  We got some good
> improvements, like adding self-tests, using "N" as "just another number"
> that could be used anywhere, and making things not CPU specific.
> 
> But now it is time to close this review out since is down to just
> hand-wringing over hypothetical use cases, bikeshedding on upper/lower
> case, and a wild goose chase on trying to avoid adding a function arg.
> 
> So, once again - thanks to all who provided input; it was all considered
> even if not all of it was used.  And in that vein, just to be clear:
> 
> 1) There will be no adaptive modifying or guessing what the user meant if
> a range turns out to be invalid.  The caller will be responsible for
> handling the -EINVAL just as things are currently today.
> 
> 2) There will be no use of "L" or lower case "n" because there is simply
> no need for it.  Yes, it would be simple enough to add, but it complicates
> things and would also be impossible to remove later, once it went mainline.
> 
> 
> The original text from v4 follows:
> 
> The basic objective here was to add support for "nohz_full=8-N" and/or
> "rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference
> to the last core, evaluated at boot for anything using a CPU list.
> 
> The thinking behind this, is that people carve off a few early CPUs to
> support housekeeping tasks, and perhaps dedicate one to a busy I/O
> peripheral, and then the remaining pool of CPUs out to the end are a
> part of a commonly configured pool used for the real work the user
> cares about.
> 
> Extend that logic out to a fleet of machines - some new, and some
> nearing EOL, and you've probably got a wide range of core counts to
> contend with - even though the early number of cores dedicated to the
> system overhead probably doesn't vary.
> 
> This change would enable sysadmins to have a common bootarg across all
> such systems, and would also avoid any off-by-one fencepost errors that
> happen for users who might briefly forget that core counts start at zero.
> 
> Originally I did this at the CPU subsys level, but Yury suggested it
> be moved down further to bitmap level itself, which made the core 
> implementation smaller and less complex, but the series longer.
> 
> New self tests are added to better exercise what bitmap range/region
> currently supports, and new tests are added for the new "N" support.
> 
> Also tested boot arg and the post-boot cgroup use case as per below:
> 
>    root@hackbox:~# cat /proc/cmdline 
>    BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2
>    root@hackbox:~# dmesg|grep Offl
>    rcu:     Offload RCU callbacks from CPUs: 2-3,8,10,12,14.
> 
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
>    
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
>    10-15
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus
>    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
>    15
> 
> This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file.
> 
> Note that "N" is a dynamic quantity, and can change scope if the bitmap
> is changed in size.  So at the risk of stating the obvious, don't use it
> for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff.
> 
> Paul.
> ---

Acked-by: Yury Norov <yury.norov@gmail.com>
 
> [v5: go back to v3 location of "nbits" in region.  Add acks/reviewed.]
> 
> [v4: pair nbits with region, instead of inside it.  Split EINVAL and
>  ERANGE tests.  Don't handle start/end/offset within a macro to
>  abstract away nbits usage.  Added some Reviwed-by/Ack tags.]
>  https://lore.kernel.org/lkml/20210209225907.78405-1-paul.gortmaker@windriver.com/
> 
> [v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs.
>  just being allowed at end of range like "0-N".  Add new self-tests.  Drop
>  "all" and "none" aliases as redundant and not worth the extra complication. ]
>  https://lore.kernel.org/lkml/20210126171141.122639-1-paul.gortmaker@windriver.com/
> 
> [v2: push code down from cpu subsys to core bitmap code as per
>  Yury's comments.  Change "last" to simply be "N" as per PeterZ.]
>  https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/
> 
> [v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/
> 
> Cc: Li Zefan <lizefan@huawei.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> 
> 
> 
> Paul Gortmaker (8):
>   lib: test_bitmap: clearly separate ERANGE from EINVAL tests.
>   lib: test_bitmap: add tests to trigger ERANGE case.
>   lib: test_bitmap: add more start-end:offset/len tests
>   lib: bitmap: fold nbits into region struct
>   lib: bitmap: move ERANGE check from set_region to check_region
>   lib: bitmap: support "N" as an alias for size of bitmap
>   lib: test_bitmap: add tests for "N" alias
>   rcu: deprecate "all" option to rcu_nocbs=
> 
>  .../admin-guide/kernel-parameters.rst         |  7 +++
>  .../admin-guide/kernel-parameters.txt         |  4 +-
>  kernel/rcu/tree_plugin.h                      |  6 +--
>  lib/bitmap.c                                  | 49 +++++++++++--------
>  lib/test_bitmap.c                             | 46 ++++++++++++++---
>  5 files changed, 79 insertions(+), 33 deletions(-)
> 
> -- 
> 2.30.0

Re: [PATCH v5 0/8] support for bitmap (and hence CPU) list "N" abbreviation

[Paul E. McKenney]

On Mon, Feb 22, 2021 at 05:05:06PM -0800, Yury Norov wrote:
> On Sun, Feb 21, 2021 at 03:08:19AM -0500, Paul Gortmaker wrote:
> > This is the 5th and final version of this series.  We got some good
> > improvements, like adding self-tests, using "N" as "just another number"
> > that could be used anywhere, and making things not CPU specific.
> > 
> > But now it is time to close this review out since is down to just
> > hand-wringing over hypothetical use cases, bikeshedding on upper/lower
> > case, and a wild goose chase on trying to avoid adding a function arg.
> > 
> > So, once again - thanks to all who provided input; it was all considered
> > even if not all of it was used.  And in that vein, just to be clear:
> > 
> > 1) There will be no adaptive modifying or guessing what the user meant if
> > a range turns out to be invalid.  The caller will be responsible for
> > handling the -EINVAL just as things are currently today.
> > 
> > 2) There will be no use of "L" or lower case "n" because there is simply
> > no need for it.  Yes, it would be simple enough to add, but it complicates
> > things and would also be impossible to remove later, once it went mainline.
> > 
> > 
> > The original text from v4 follows:
> > 
> > The basic objective here was to add support for "nohz_full=8-N" and/or
> > "rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference
> > to the last core, evaluated at boot for anything using a CPU list.
> > 
> > The thinking behind this, is that people carve off a few early CPUs to
> > support housekeeping tasks, and perhaps dedicate one to a busy I/O
> > peripheral, and then the remaining pool of CPUs out to the end are a
> > part of a commonly configured pool used for the real work the user
> > cares about.
> > 
> > Extend that logic out to a fleet of machines - some new, and some
> > nearing EOL, and you've probably got a wide range of core counts to
> > contend with - even though the early number of cores dedicated to the
> > system overhead probably doesn't vary.
> > 
> > This change would enable sysadmins to have a common bootarg across all
> > such systems, and would also avoid any off-by-one fencepost errors that
> > happen for users who might briefly forget that core counts start at zero.
> > 
> > Originally I did this at the CPU subsys level, but Yury suggested it
> > be moved down further to bitmap level itself, which made the core 
> > implementation smaller and less complex, but the series longer.
> > 
> > New self tests are added to better exercise what bitmap range/region
> > currently supports, and new tests are added for the new "N" support.
> > 
> > Also tested boot arg and the post-boot cgroup use case as per below:
> > 
> >    root@hackbox:~# cat /proc/cmdline 
> >    BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2
> >    root@hackbox:~# dmesg|grep Offl
> >    rcu:     Offload RCU callbacks from CPUs: 2-3,8,10,12,14.
> > 
> >    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
> >    
> >    root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus
> >    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
> >    10-15
> >    root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus
> >    root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
> >    15
> > 
> > This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file.
> > 
> > Note that "N" is a dynamic quantity, and can change scope if the bitmap
> > is changed in size.  So at the risk of stating the obvious, don't use it
> > for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff.
> > 
> > Paul.
> > ---
> 
> Acked-by: Yury Norov <yury.norov@gmail.com>

Applied, thank you all!

							Thanx, Paul

> > [v5: go back to v3 location of "nbits" in region.  Add acks/reviewed.]
> > 
> > [v4: pair nbits with region, instead of inside it.  Split EINVAL and
> >  ERANGE tests.  Don't handle start/end/offset within a macro to
> >  abstract away nbits usage.  Added some Reviwed-by/Ack tags.]
> >  https://lore.kernel.org/lkml/20210209225907.78405-1-paul.gortmaker@windriver.com/
> > 
> > [v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs.
> >  just being allowed at end of range like "0-N".  Add new self-tests.  Drop
> >  "all" and "none" aliases as redundant and not worth the extra complication. ]
> >  https://lore.kernel.org/lkml/20210126171141.122639-1-paul.gortmaker@windriver.com/
> > 
> > [v2: push code down from cpu subsys to core bitmap code as per
> >  Yury's comments.  Change "last" to simply be "N" as per PeterZ.]
> >  https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/
> > 
> > [v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/
> > 
> > Cc: Li Zefan <lizefan@huawei.com>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Yury Norov <yury.norov@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Josh Triplett <josh@joshtriplett.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: "Paul E. McKenney" <paulmck@kernel.org>
> > Cc: Frederic Weisbecker <fweisbec@gmail.com>
> > Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > 
> > 
> > 
> > Paul Gortmaker (8):
> >   lib: test_bitmap: clearly separate ERANGE from EINVAL tests.
> >   lib: test_bitmap: add tests to trigger ERANGE case.
> >   lib: test_bitmap: add more start-end:offset/len tests
> >   lib: bitmap: fold nbits into region struct
> >   lib: bitmap: move ERANGE check from set_region to check_region
> >   lib: bitmap: support "N" as an alias for size of bitmap
> >   lib: test_bitmap: add tests for "N" alias
> >   rcu: deprecate "all" option to rcu_nocbs=
> > 
> >  .../admin-guide/kernel-parameters.rst         |  7 +++
> >  .../admin-guide/kernel-parameters.txt         |  4 +-
> >  kernel/rcu/tree_plugin.h                      |  6 +--
> >  lib/bitmap.c                                  | 49 +++++++++++--------
> >  lib/test_bitmap.c                             | 46 ++++++++++++++---
> >  5 files changed, 79 insertions(+), 33 deletions(-)
> > 
> > -- 
> > 2.30.0

[PATCH v4 0/8] support for bitmap (and hence CPU) list "N" abbreviation

[Paul Gortmaker]

The basic objective here was to add support for "nohz_full=8-N" and/or
"rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference
to the last core, evaluated at boot for anything using a CPU list.

The thinking behind this, is that people carve off a few early CPUs to
support housekeeping tasks, and perhaps dedicate one to a busy I/O
peripheral, and then the remaining pool of CPUs out to the end are a
part of a commonly configured pool used for the real work the user
cares about.

Extend that logic out to a fleet of machines - some new, and some
nearing EOL, and you've probably got a wide range of core counts to
contend with - even though the early number of cores dedicated to the
system overhead probably doesn't vary.

This change would enable sysadmins to have a common bootarg across all
such systems, and would also avoid any off-by-one fencepost errors that
happen for users who might briefly forget that core counts start at zero.

Originally I did this at the CPU subsys level, but Yury suggested it
be moved down further to bitmap level itself, which made the core 
implementation smaller and less complex, but the series longer.

New self tests are added to better exercise what bitmap range/region
currently supports, and new tests are added for the new "N" support.

Also tested boot arg and the post-boot cgroup use case as per below:

   root@hackbox:~# cat /proc/cmdline 
   BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2
   root@hackbox:~# dmesg|grep Offl
   rcu:     Offload RCU callbacks from CPUs: 2-3,8,10,12,14.

   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   
   root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus
   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   10-15
   root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus
   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   15

This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file.

Note that "N" is a dynamic quantity, and can change scope if the bitmap
is changed in size.  So at the risk of stating the obvious, don't use it
for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff.

Paul.
---

I've intentionally not gone down the rabbit hole of whether N or Z or
L is the better letter to mark the end of a mathematical set in the
hope that we can stay focused, and get this closed out here in v4.

Aside from that, I believe all other feedback has been responded to
in one way or another.  Note that I didn't add Reviewed/Ack tags to
anything that changed significantly from what was reviewed in v3.

[v4: pair nbits with region, instead of inside it.  Split EINVAL and
 ERANGE tests.  Don't handle start/end/offset within a macro to
 abstract away nbits usage.  Added some Reviwed-by/Ack tags.]

[v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs.
 just being allowed at end of range like "0-N".  Add new self-tests.  Drop
 "all" and "none" aliases as redundant and not worth the extra complication. ]
 https://lore.kernel.org/lkml/20210126171141.122639-1-paul.gortmaker@windriver.com

[v2: push code down from cpu subsys to core bitmap code as per
 Yury's comments.  Change "last" to simply be "N" as per PeterZ.]
 https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/

[v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/

Cc: Li Zefan <lizefan@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>


Paul Gortmaker (8):
  lib: test_bitmap: clearly separate ERANGE from EINVAL tests.
  lib: test_bitmap: add tests to trigger ERANGE case.
  lib: test_bitmap: add more start-end:offset/len tests
  lib: bitmap: move ERANGE check from set_region to check_region
  lib: bitmap: pair nbits value with region struct
  lib: bitmap: support "N" as an alias for size of bitmap
  lib: test_bitmap: add tests for "N" alias
  rcu: deprecate "all" option to rcu_nocbs=

 .../admin-guide/kernel-parameters.rst         |  7 +++
 .../admin-guide/kernel-parameters.txt         |  4 +-
 kernel/rcu/tree_plugin.h                      |  6 +-
 lib/bitmap.c                                  | 62 +++++++++++++------
 lib/test_bitmap.c                             | 46 ++++++++++++--
 5 files changed, 93 insertions(+), 32 deletions(-)

-- 
2.17.1

[PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Paul Gortmaker]

While this is done for all bitmaps, the original use case in mind was
for CPU masks and cpulist_parse() as described below.

It seems that a common configuration is to use the 1st couple cores for
housekeeping tasks.  This tends to leave the remaining ones to form a
pool of similarly configured cores to take on the real workload of
interest to the user.

So on machine A - with 32 cores, it could be 0-3 for "system" and then
4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
setting up the worker pool of CPUs.

But then newer machine B is added, and it has 48 cores, and so while
the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.

Multiple deployment becomes easier when we can just simply replace 31
and 47 with "N" and let the system substitute in the actual number at
boot; a number that it knows better than we do.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Yury Norov <yury.norov@gmail.com> # move it from CPU code
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 .../admin-guide/kernel-parameters.rst         |  7 +++++
 lib/bitmap.c                                  | 27 ++++++++++++++-----
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index 682ab28b5c94..7733a773f5f8 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -68,6 +68,13 @@ For example one can add to the command line following parameter:
 
 where the final item represents CPUs 100,101,125,126,150,151,...
 
+The value "N" can be used to represent the numerically last CPU on the system,
+i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
+
+Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
+to change, such as less cores in the CPU list, then N and any ranges using N
+will also change.  Use the same on a small 4 core system, and "16-N" becomes
+"16-3" and now the same boot input will be flagged as invalid (start > end).
 
 
 This document may not be entirely up to date and comprehensive. The command
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 6b568f98af3d..cc7cb1fca1ac 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -530,11 +530,17 @@ static int bitmap_check_region(const struct bitmap_region *br)
 	return 0;
 }
 
-static const char *bitmap_getnum(const char *str, unsigned int *num)
+static const char *bitmap_getnum(const char *str, unsigned int *num,
+				 unsigned int lastbit)
 {
 	unsigned long long n;
 	unsigned int len;
 
+	if (str[0] == 'N') {
+		*num = lastbit;
+		return str + 1;
+	}
+
 	len = _parse_integer(str, 10, &n);
 	if (!len)
 		return ERR_PTR(-EINVAL);
@@ -580,9 +586,12 @@ static const char *bitmap_find_region_reverse(const char *start, const char *end
 	return end;
 }
 
-static const char *bitmap_parse_region(const char *str, struct region *r)
+static const char *bitmap_parse_region(const char *str, struct bitmap_region *br)
 {
-	str = bitmap_getnum(str, &r->start);
+	struct region *r = br->r;
+	unsigned int lastbit = br->nbits - 1;
+
+	str = bitmap_getnum(str, &r->start, lastbit);
 	if (IS_ERR(str))
 		return str;
 
@@ -592,7 +601,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
 	if (*str != '-')
 		return ERR_PTR(-EINVAL);
 
-	str = bitmap_getnum(str + 1, &r->end);
+	str = bitmap_getnum(str + 1, &r->end, lastbit);
 	if (IS_ERR(str))
 		return str;
 
@@ -602,14 +611,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
 	if (*str != ':')
 		return ERR_PTR(-EINVAL);
 
-	str = bitmap_getnum(str + 1, &r->off);
+	str = bitmap_getnum(str + 1, &r->off, lastbit);
 	if (IS_ERR(str))
 		return str;
 
 	if (*str != '/')
 		return ERR_PTR(-EINVAL);
 
-	return bitmap_getnum(str + 1, &r->group_len);
+	return bitmap_getnum(str + 1, &r->group_len, lastbit);
 
 no_end:
 	r->end = r->start;
@@ -636,6 +645,10 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
  * From each group will be used only defined amount of bits.
  * Syntax: range:used_size/group_size
  * Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769
+ * The value 'N' can be used as a dynamically substituted token for the
+ * maximum allowed value; i.e (nmaskbits - 1).  Keep in mind that it is
+ * dynamic, so if system changes cause the bitmap width to change, such
+ * as more cores in a CPU list, then any ranges using N will also change.
  *
  * Returns: 0 on success, -errno on invalid input strings. Error values:
  *
@@ -660,7 +673,7 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
 		if (buf == NULL)
 			return 0;
 
-		buf = bitmap_parse_region(buf, &r);
+		buf = bitmap_parse_region(buf, &br);
 		if (IS_ERR(buf))
 			return PTR_ERR(buf);
 
-- 
2.17.1

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Yury Norov]

On Tue, Feb 9, 2021 at 3:01 PM Paul Gortmaker
<paul.gortmaker@windriver.com> wrote:
>
> While this is done for all bitmaps, the original use case in mind was
> for CPU masks and cpulist_parse() as described below.
>
> It seems that a common configuration is to use the 1st couple cores for
> housekeeping tasks.  This tends to leave the remaining ones to form a
> pool of similarly configured cores to take on the real workload of
> interest to the user.
>
> So on machine A - with 32 cores, it could be 0-3 for "system" and then
> 4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
> setting up the worker pool of CPUs.
>
> But then newer machine B is added, and it has 48 cores, and so while
> the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.
>
> Multiple deployment becomes easier when we can just simply replace 31
> and 47 with "N" and let the system substitute in the actual number at
> boot; a number that it knows better than we do.
>
> Cc: Yury Norov <yury.norov@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Suggested-by: Yury Norov <yury.norov@gmail.com> # move it from CPU code
> Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
> ---
>  .../admin-guide/kernel-parameters.rst         |  7 +++++
>  lib/bitmap.c                                  | 27 ++++++++++++++-----
>  2 files changed, 27 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
> index 682ab28b5c94..7733a773f5f8 100644
> --- a/Documentation/admin-guide/kernel-parameters.rst
> +++ b/Documentation/admin-guide/kernel-parameters.rst
> @@ -68,6 +68,13 @@ For example one can add to the command line following parameter:
>
>  where the final item represents CPUs 100,101,125,126,150,151,...
>
> +The value "N" can be used to represent the numerically last CPU on the system,
> +i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
> +
> +Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
> +to change, such as less cores in the CPU list, then N and any ranges using N
> +will also change.  Use the same on a small 4 core system, and "16-N" becomes
> +"16-3" and now the same boot input will be flagged as invalid (start > end).
>
>
>  This document may not be entirely up to date and comprehensive. The command
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 6b568f98af3d..cc7cb1fca1ac 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -530,11 +530,17 @@ static int bitmap_check_region(const struct bitmap_region *br)
>         return 0;
>  }
>
> -static const char *bitmap_getnum(const char *str, unsigned int *num)
> +static const char *bitmap_getnum(const char *str, unsigned int *num,
> +                                unsigned int lastbit)

The idea of struct bitmap_region is avoid passing the lastbit to the functions.
But here you do pass. Can you please be consistent? Or if I misunderstand
the idea of struct bitmap_region, can you please clarify it?

Also, I don't think that in this specific case it's worth it to create
a hierarchy of
structures. Just adding lastbits to struct region will be simpler and more
transparent.

>  {
>         unsigned long long n;
>         unsigned int len;
>
> +       if (str[0] == 'N') {
> +               *num = lastbit;
> +               return str + 1;
> +       }
> +
>         len = _parse_integer(str, 10, &n);
>         if (!len)
>                 return ERR_PTR(-EINVAL);
> @@ -580,9 +586,12 @@ static const char *bitmap_find_region_reverse(const char *start, const char *end
>         return end;
>  }
>
> -static const char *bitmap_parse_region(const char *str, struct region *r)
> +static const char *bitmap_parse_region(const char *str, struct bitmap_region *br)

It seems like you declare struct bitmap_region in patch 8, but use it
in patch 6.
Can you please reorder your patches and resubmit?

>  {
> -       str = bitmap_getnum(str, &r->start);
> +       struct region *r = br->r;
> +       unsigned int lastbit = br->nbits - 1;
> +
> +       str = bitmap_getnum(str, &r->start, lastbit);
>         if (IS_ERR(str))
>                 return str;
>
> @@ -592,7 +601,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
>         if (*str != '-')
>                 return ERR_PTR(-EINVAL);
>
> -       str = bitmap_getnum(str + 1, &r->end);
> +       str = bitmap_getnum(str + 1, &r->end, lastbit);
>         if (IS_ERR(str))
>                 return str;
>
> @@ -602,14 +611,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
>         if (*str != ':')
>                 return ERR_PTR(-EINVAL);
>
> -       str = bitmap_getnum(str + 1, &r->off);
> +       str = bitmap_getnum(str + 1, &r->off, lastbit);
>         if (IS_ERR(str))
>                 return str;
>
>         if (*str != '/')
>                 return ERR_PTR(-EINVAL);
>
> -       return bitmap_getnum(str + 1, &r->group_len);
> +       return bitmap_getnum(str + 1, &r->group_len, lastbit);
>
>  no_end:
>         r->end = r->start;
> @@ -636,6 +645,10 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
>   * From each group will be used only defined amount of bits.
>   * Syntax: range:used_size/group_size
>   * Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769
> + * The value 'N' can be used as a dynamically substituted token for the
> + * maximum allowed value; i.e (nmaskbits - 1).  Keep in mind that it is
> + * dynamic, so if system changes cause the bitmap width to change, such
> + * as more cores in a CPU list, then any ranges using N will also change.
>   *
>   * Returns: 0 on success, -errno on invalid input strings. Error values:
>   *
> @@ -660,7 +673,7 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
>                 if (buf == NULL)
>                         return 0;
>
> -               buf = bitmap_parse_region(buf, &r);
> +               buf = bitmap_parse_region(buf, &br);
>                 if (IS_ERR(buf))
>                         return PTR_ERR(buf);
>
> --
> 2.17.1
>

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Paul Gortmaker]

[Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap] On 09/02/2021 (Tue 15:16) Yury Norov wrote:

> On Tue, Feb 9, 2021 at 3:01 PM Paul Gortmaker
> <paul.gortmaker@windriver.com> wrote:

[...]

> >
> > -static const char *bitmap_getnum(const char *str, unsigned int *num)
> > +static const char *bitmap_getnum(const char *str, unsigned int *num,
> > +                                unsigned int lastbit)
> 
> The idea of struct bitmap_region is avoid passing the lastbit to the functions.
> But here you do pass. Can you please be consistent? Or if I misunderstand
> the idea of struct bitmap_region, can you please clarify it?
> 
> Also, I don't think that in this specific case it's worth it to create
> a hierarchy of
> structures. Just adding lastbits to struct region will be simpler and more
> transparent.

I'm getting mixed messages from different people as to what is wanted here.

Here is what the code looks like now; only relevant lines shown:

 -------------------------------
int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
{

        struct region r;

        bitmap_parse_region(buf, &r);       <-----------
        bitmap_check_region(&r);
        bitmap_set_region(&r, maskp, nmaskbits);
}

static const char *bitmap_parse_region(const char *str, struct region *r)
{
        bitmap_getnum(str, &r->start);
        bitmap_getnum(str + 1, &r->end);
        bitmap_getnum(str + 1, &r->off);
        bitmap_getnum(str + 1, &r->group_len);
}

static const char *bitmap_getnum(const char *str, unsigned int *num)
{
	/* PG: We need nmaskbits here for N processing. */
}
 -------------------------------


Note the final function - the one where you asked to locate the N
processing into -- does not take a region.  So even if we bundle nbits
into the region struct, it doesn't get the data to where we need it.

Choices:

1) pass in nbits just like bitmap_set_region() does currently.

2) add nbits to region and pass full region instead of start/end/off.

2a) add nbits to region and pass full region and also start/end/off.

3) use *num as a bi-directional data path and initialize with nbits.


Yury doesn't want us add any function args -- i.e. not to do #1.

Andy didn't like #2 because it "hides" that we are writing to r.

I ruled out sending 2a -- bitmap_getnum(str, r, &r->end)  because
it adds an arg, AND seems rather redundant to pass r and r->field.

The #3 is the smallest change - but seems like we are trying to be
too clever just to save a line of code or a couple bytes. (see below)

Yury - in your reply to patch 5, you indicate you wrote the region
code and want me to go back to putting nbits into region directly.

Can you guys please clarify who is maintainer and hence exactly how
you want this relatively minor detail handled?  I'll gladly do it
in whatever way the maintainer wants just to get this finally done.

I'd rather not keep going in circles and guessing and annoying everyone
else on the Cc: list by filling their inbox any more than I already have.

That would help a lot in getting this finished.

Thanks,
Paul.
--

Example #3 -- not sent..

+#define DECLARE_REGION(rname, initval) \
+struct region rname = {                \
+       .start = initval,               \
+       .off = initval,                 \
+       .group_len = initval,           \
+       .end = initval,                 \
+}

[...]

-       struct region r;
+       DECLARE_REGION(r, nmaskbits - 1);       /* "N-N:N/N" */

[...]

+/*
+ * Seeing 'N' tells us to leave the value of "num" unchanged (which will
+ * be the max value for the width of the bitmap, set via DECLARE_REGION).
+ */
 static const char *bitmap_getnum(const char *str, unsigned int *num)
 {
        unsigned long long n;
        unsigned int len;
 
+       if (str[0] == 'N')      /* nothing to do, just advance str */
+               return str + 1;

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Andy Shevchenko]

On Wed, Feb 10, 2021 at 10:58:25AM -0500, Paul Gortmaker wrote:
> [Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap] On 09/02/2021 (Tue 15:16) Yury Norov wrote:
> 
> > On Tue, Feb 9, 2021 at 3:01 PM Paul Gortmaker
> > <paul.gortmaker@windriver.com> wrote:
> 
> [...]
> 
> > > -static const char *bitmap_getnum(const char *str, unsigned int *num)
> > > +static const char *bitmap_getnum(const char *str, unsigned int *num,
> > > +                                unsigned int lastbit)
> > 
> > The idea of struct bitmap_region is avoid passing the lastbit to the functions.
> > But here you do pass. Can you please be consistent? Or if I misunderstand
> > the idea of struct bitmap_region, can you please clarify it?
> > 
> > Also, I don't think that in this specific case it's worth it to create
> > a hierarchy of
> > structures. Just adding lastbits to struct region will be simpler and more
> > transparent.
> 
> I'm getting mixed messages from different people as to what is wanted here.
> 
> Here is what the code looks like now; only relevant lines shown:
> 
>  -------------------------------
> int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
> {
> 
>         struct region r;
> 
>         bitmap_parse_region(buf, &r);       <-----------
>         bitmap_check_region(&r);
>         bitmap_set_region(&r, maskp, nmaskbits);
> }
> 
> static const char *bitmap_parse_region(const char *str, struct region *r)
> {
>         bitmap_getnum(str, &r->start);
>         bitmap_getnum(str + 1, &r->end);
>         bitmap_getnum(str + 1, &r->off);
>         bitmap_getnum(str + 1, &r->group_len);
> }
> 
> static const char *bitmap_getnum(const char *str, unsigned int *num)
> {
> 	/* PG: We need nmaskbits here for N processing. */
> }
>  -------------------------------
> 
> 
> Note the final function - the one where you asked to locate the N
> processing into -- does not take a region.  So even if we bundle nbits
> into the region struct, it doesn't get the data to where we need it.
> 
> Choices:
> 
> 1) pass in nbits just like bitmap_set_region() does currently.
> 
> 2) add nbits to region and pass full region instead of start/end/off.
> 
> 2a) add nbits to region and pass full region and also start/end/off.
> 
> 3) use *num as a bi-directional data path and initialize with nbits.
> 
> 
> Yury doesn't want us add any function args -- i.e. not to do #1.
> 
> Andy didn't like #2 because it "hides" that we are writing to r.
> 
> I ruled out sending 2a -- bitmap_getnum(str, r, &r->end)  because
> it adds an arg, AND seems rather redundant to pass r and r->field.
> 
> The #3 is the smallest change - but seems like we are trying to be
> too clever just to save a line of code or a couple bytes. (see below)
> 
> Yury - in your reply to patch 5, you indicate you wrote the region
> code and want me to go back to putting nbits into region directly.
> 
> Can you guys please clarify who is maintainer and hence exactly how
> you want this relatively minor detail handled?  I'll gladly do it
> in whatever way the maintainer wants just to get this finally done.

Funny that there is no maintainer of the code.
That said, I consider #1 or #3 is good enough. Rationale for
- #1: it doesn't touch purity of getnum(), I think it's good enough not to know
  region details
- #3 (as you posted below): I like how it looks like (one nit below, though)

But let's put this way, I think Yury had done a lot in the area, let's listen
more to him than to me.

> I'd rather not keep going in circles and guessing and annoying everyone
> else on the Cc: list by filling their inbox any more than I already have.
> 
> That would help a lot in getting this finished.

Agree!

> Example #3 -- not sent..
> 
> +#define DECLARE_REGION(rname, initval) \
> +struct region rname = {                \
> +       .start = initval,               \
> +       .off = initval,                 \
> +       .group_len = initval,           \
> +       .end = initval,                 \
> +}
> 
> [...]
> 
> -       struct region r;
> +       DECLARE_REGION(r, nmaskbits - 1);       /* "N-N:N/N" */

I would initialize with nmaskbits to be sure the value is invalid, but it will
add some code, below, so up to you, guys.

> +/*
> + * Seeing 'N' tells us to leave the value of "num" unchanged (which will
> + * be the max value for the width of the bitmap, set via DECLARE_REGION).
> + */
>  static const char *bitmap_getnum(const char *str, unsigned int *num)
>  {
>         unsigned long long n;
>         unsigned int len;
>  
> +       if (str[0] == 'N')      /* nothing to do, just advance str */
> +               return str + 1;
> 

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Yury Norov]

On Wed, Feb 10, 2021 at 06:49:30PM +0200, Andy Shevchenko wrote:
> On Wed, Feb 10, 2021 at 10:58:25AM -0500, Paul Gortmaker wrote:
> > [Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap] On 09/02/2021 (Tue 15:16) Yury Norov wrote:
> > 
> > > On Tue, Feb 9, 2021 at 3:01 PM Paul Gortmaker
> > > <paul.gortmaker@windriver.com> wrote:
> > 
> > [...]
> > 
> > > > -static const char *bitmap_getnum(const char *str, unsigned int *num)
> > > > +static const char *bitmap_getnum(const char *str, unsigned int *num,
> > > > +                                unsigned int lastbit)
> > > 
> > > The idea of struct bitmap_region is avoid passing the lastbit to the functions.
> > > But here you do pass. Can you please be consistent? Or if I misunderstand
> > > the idea of struct bitmap_region, can you please clarify it?
> > > 
> > > Also, I don't think that in this specific case it's worth it to create
> > > a hierarchy of
> > > structures. Just adding lastbits to struct region will be simpler and more
> > > transparent.
> > 
> > I'm getting mixed messages from different people as to what is wanted here.
> > 
> > Here is what the code looks like now; only relevant lines shown:
> > 
> >  -------------------------------
> > int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
> > {
> > 
> >         struct region r;
> > 
> >         bitmap_parse_region(buf, &r);       <-----------
> >         bitmap_check_region(&r);
> >         bitmap_set_region(&r, maskp, nmaskbits);
> > }
> > 
> > static const char *bitmap_parse_region(const char *str, struct region *r)
> > {
> >         bitmap_getnum(str, &r->start);
> >         bitmap_getnum(str + 1, &r->end);
> >         bitmap_getnum(str + 1, &r->off);
> >         bitmap_getnum(str + 1, &r->group_len);
> > }
> > 
> > static const char *bitmap_getnum(const char *str, unsigned int *num)
> > {
> > 	/* PG: We need nmaskbits here for N processing. */
> > }
> >  -------------------------------
> > 
> > 
> > Note the final function - the one where you asked to locate the N
> > processing into -- does not take a region.  So even if we bundle nbits
> > into the region struct, it doesn't get the data to where we need it.
> > 
> > Choices:
> > 
> > 1) pass in nbits just like bitmap_set_region() does currently.
> > 
> > 2) add nbits to region and pass full region instead of start/end/off.
> > 
> > 2a) add nbits to region and pass full region and also start/end/off.
> > 
> > 3) use *num as a bi-directional data path and initialize with nbits.
> > 
> > 
> > Yury doesn't want us add any function args -- i.e. not to do #1.
> > 
> > Andy didn't like #2 because it "hides" that we are writing to r.
> > 
> > I ruled out sending 2a -- bitmap_getnum(str, r, &r->end)  because
> > it adds an arg, AND seems rather redundant to pass r and r->field.
> > 
> > The #3 is the smallest change - but seems like we are trying to be
> > too clever just to save a line of code or a couple bytes. (see below)
> > 
> > Yury - in your reply to patch 5, you indicate you wrote the region
> > code and want me to go back to putting nbits into region directly.
> > 
> > Can you guys please clarify who is maintainer and hence exactly how
> > you want this relatively minor detail handled?  I'll gladly do it
> > in whatever way the maintainer wants just to get this finally done.
> 
> Funny that there is no maintainer of the code.
> That said, I consider #1 or #3 is good enough. Rationale for
> - #1: it doesn't touch purity of getnum(), I think it's good enough not to know
>   region details
> - #3 (as you posted below): I like how it looks like (one nit below, though)
> 
> But let's put this way, I think Yury had done a lot in the area, let's listen
> more to him than to me.

I think that the simplest approach is the best. For me, the simplest
thing is to add a field to existing structure, like this:

        struct region {
                unsigned int start;
                unsigned int off; 
                unsigned int group_len;
                unsigned int end; 
                unsigned int nbits; 
        };

Of course we can do like:
 
        struct region {
                struct boundaries;
                struct periodic_part;
        };

        struct bitmap_region {
                struct region;
                unsigned int nbits; 
        };

But it would be nothing better than simple flat structure.

> > I'd rather not keep going in circles and guessing and annoying everyone
> > else on the Cc: list by filling their inbox any more than I already have.
> > 
> > That would help a lot in getting this finished.
> 
> Agree!
> 
> > Example #3 -- not sent..
> > 
> > +#define DECLARE_REGION(rname, initval) \
> > +struct region rname = {                \
> > +       .start = initval,               \
> > +       .off = initval,                 \
> > +       .group_len = initval,           \
> > +       .end = initval,                 \
> > +}
> > 
> > [...]
> > 
> > -       struct region r;
> > +       DECLARE_REGION(r, nmaskbits - 1);       /* "N-N:N/N" */
>
> I would initialize with nmaskbits to be sure the value is invalid, but it will
> add some code, below, so up to you, guys.

We don't need to initialize r because it's purely internal and helpers
don't expect that r is initialized, so it's waste of cycles.
 
> > +/*
> > + * Seeing 'N' tells us to leave the value of "num" unchanged (which will
> > + * be the max value for the width of the bitmap, set via DECLARE_REGION).
> > + */
> >  static const char *bitmap_getnum(const char *str, unsigned int *num)
> >  {
> >         unsigned long long n;
> >         unsigned int len;
> >  
> > +       if (str[0] == 'N')      /* nothing to do, just advance str */
> > +               return str + 1;

Is my understanding correct that this is an attempt to avoid adding
the nbits to struct region? It would probably work, but I'd prefer
to extend the structure. For me it's more readable and maintainable
approach.

Yury

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Paul Gortmaker]

[Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap] On 11/02/2021 (Thu 17:24) Yury Norov wrote:

> On Wed, Feb 10, 2021 at 06:49:30PM +0200, Andy Shevchenko wrote:
> > On Wed, Feb 10, 2021 at 10:58:25AM -0500, Paul Gortmaker wrote:
> > > [Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap] On 09/02/2021 (Tue 15:16) Yury Norov wrote:
> > > 
> > > > On Tue, Feb 9, 2021 at 3:01 PM Paul Gortmaker
> > > > <paul.gortmaker@windriver.com> wrote:
> > > 
> > > [...]
> > > 
> > > > > -static const char *bitmap_getnum(const char *str, unsigned int *num)
> > > > > +static const char *bitmap_getnum(const char *str, unsigned int *num,
> > > > > +                                unsigned int lastbit)
> > > > 
> > > > The idea of struct bitmap_region is avoid passing the lastbit to the functions.
> > > > But here you do pass. Can you please be consistent? Or if I misunderstand
> > > > the idea of struct bitmap_region, can you please clarify it?
> > > > 
> > > > Also, I don't think that in this specific case it's worth it to create
> > > > a hierarchy of
> > > > structures. Just adding lastbits to struct region will be simpler and more
> > > > transparent.
> > > 
> > > I'm getting mixed messages from different people as to what is wanted here.
> > > 
> > > Here is what the code looks like now; only relevant lines shown:
> > > 
> > >  -------------------------------
> > > int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
> > > {
> > > 
> > >         struct region r;
> > > 
> > >         bitmap_parse_region(buf, &r);       <-----------
> > >         bitmap_check_region(&r);
> > >         bitmap_set_region(&r, maskp, nmaskbits);
> > > }
> > > 
> > > static const char *bitmap_parse_region(const char *str, struct region *r)
> > > {
> > >         bitmap_getnum(str, &r->start);
> > >         bitmap_getnum(str + 1, &r->end);
> > >         bitmap_getnum(str + 1, &r->off);
> > >         bitmap_getnum(str + 1, &r->group_len);
> > > }
> > > 
> > > static const char *bitmap_getnum(const char *str, unsigned int *num)
> > > {
> > > 	/* PG: We need nmaskbits here for N processing. */
> > > }
> > >  -------------------------------
> > > 
> > > 
> > > Note the final function - the one where you asked to locate the N
> > > processing into -- does not take a region.  So even if we bundle nbits
> > > into the region struct, it doesn't get the data to where we need it.

Yury - you asked why there was an arg passed -- "lastbit"  -- and from
your reply, I don't think you fully read my answer - or at least missed
the three key sentences above as to why "lastbit" was passed.

> > > 
> > > Choices:
> > > 
> > > 1) pass in nbits just like bitmap_set_region() does currently.
> > > 
> > > 2) add nbits to region and pass full region instead of start/end/off.
> > > 
> > > 2a) add nbits to region and pass full region and also start/end/off.
> > > 
> > > 3) use *num as a bi-directional data path and initialize with nbits.
> > > 
> > > 
> > > Yury doesn't want us add any function args -- i.e. not to do #1.
> > > 
> > > Andy didn't like #2 because it "hides" that we are writing to r.
> > > 
> > > I ruled out sending 2a -- bitmap_getnum(str, r, &r->end)  because
> > > it adds an arg, AND seems rather redundant to pass r and r->field.
> > > 
> > > The #3 is the smallest change - but seems like we are trying to be
> > > too clever just to save a line of code or a couple bytes. (see below)
> > > 
> > > Yury - in your reply to patch 5, you indicate you wrote the region
> > > code and want me to go back to putting nbits into region directly.
> > > 
> > > Can you guys please clarify who is maintainer and hence exactly how
> > > you want this relatively minor detail handled?  I'll gladly do it
> > > in whatever way the maintainer wants just to get this finally done.
> > 
> > Funny that there is no maintainer of the code.
> > That said, I consider #1 or #3 is good enough. Rationale for
> > - #1: it doesn't touch purity of getnum(), I think it's good enough not to know
> >   region details
> > - #3 (as you posted below): I like how it looks like (one nit below, though)
> > 
> > But let's put this way, I think Yury had done a lot in the area, let's listen
> > more to him than to me.
> 
> I think that the simplest approach is the best. For me, the simplest
> thing is to add a field to existing structure, like this:
> 
>         struct region {
>                 unsigned int start;
>                 unsigned int off; 
>                 unsigned int group_len;
>                 unsigned int end; 
>                 unsigned int nbits; 
>         };

This is what was in v3 of this series, and I have put it back to this.

But as stated above, it doesn't get nbits to where it is needed, so
there still needs to be this one change you explicitly asked about:

 -static const char *bitmap_getnum(const char *str, unsigned int *num)
 +static const char *bitmap_getnum(const char *str, unsigned int *num,
 +                                 unsigned int lastbit)

There is no region here, so there is no access to nbits via region.
Hence the extra arg. So that is what v5 of the series will do - just
like v4 did.

Paul.
--

> 
> Of course we can do like:
>  
>         struct region {
>                 struct boundaries;
>                 struct periodic_part;
>         };
> 
>         struct bitmap_region {
>                 struct region;
>                 unsigned int nbits; 
>         };
> 
> But it would be nothing better than simple flat structure.
> 
> > > I'd rather not keep going in circles and guessing and annoying everyone
> > > else on the Cc: list by filling their inbox any more than I already have.
> > > 
> > > That would help a lot in getting this finished.
> > 
> > Agree!
> > 
> > > Example #3 -- not sent..
> > > 
> > > +#define DECLARE_REGION(rname, initval) \
> > > +struct region rname = {                \
> > > +       .start = initval,               \
> > > +       .off = initval,                 \
> > > +       .group_len = initval,           \
> > > +       .end = initval,                 \
> > > +}
> > > 
> > > [...]
> > > 
> > > -       struct region r;
> > > +       DECLARE_REGION(r, nmaskbits - 1);       /* "N-N:N/N" */
> >
> > I would initialize with nmaskbits to be sure the value is invalid, but it will
> > add some code, below, so up to you, guys.
> 
> We don't need to initialize r because it's purely internal and helpers
> don't expect that r is initialized, so it's waste of cycles.
>  
> > > +/*
> > > + * Seeing 'N' tells us to leave the value of "num" unchanged (which will
> > > + * be the max value for the width of the bitmap, set via DECLARE_REGION).
> > > + */
> > >  static const char *bitmap_getnum(const char *str, unsigned int *num)
> > >  {
> > >         unsigned long long n;
> > >         unsigned int len;
> > >  
> > > +       if (str[0] == 'N')      /* nothing to do, just advance str */
> > > +               return str + 1;
> 
> Is my understanding correct that this is an attempt to avoid adding
> the nbits to struct region? It would probably work, but I'd prefer
> to extend the structure. For me it's more readable and maintainable
> approach.
> 
> Yury

[PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation

[Paul Gortmaker]

The basic objective here was to add support for "nohz_full=8-N" and/or
"rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference
to the last core, evaluated at boot for anything using a CPU list.

The thinking behind this, is that people carve off a few early CPUs to
support housekeeping tasks, and perhaps dedicate one to a busy I/O
peripheral, and then the remaining pool of CPUs out to the end are a
part of a commonly configured pool used for the real work the user
cares about.

Extend that logic out to a fleet of machines - some new, and some
nearing EOL, and you've probably got a wide range of core counts to
contend with - even though the early number of cores dedicated to the
system overhead probably doesn't vary.

This change would enable sysadmins to have a common bootarg across all
such systems, and would also avoid any off-by-one fencepost errors that
happen for users who might briefly forget that core counts start at zero.

Originally I did this at the CPU subsys level, but Yury suggested it
be moved down further to bitmap level itself, which made the core 
implementation [6/8] smaller and less complex, but the series longer.

New self tests are added to better exercise what bitmap range/region
currently supports, and new tests are added for the new "N" support.

Also tested boot arg and the post-boot cgroup use case as per below:

   root@hackbox:~# cat /proc/cmdline 
   BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2
   root@hackbox:~# dmesg|grep Offl
   rcu:     Offload RCU callbacks from CPUs: 2-3,8,10,12,14.

   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   
   root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus
   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   10-15
   root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus
   root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
   15

This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file.

Note that "N" is a dynamic quantity, and can change scope if the bitmap
is changed in size.  So at the risk of stating the obvious, don't use it
for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff.

Paul.
---

[v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/

[v2: push code down from cpu subsys to core bitmap code as per
 Yury's comments.  Change "last" to simply be "N" as per PeterZ.]
 https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/

[v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs.
 just being allowed at end of range like "0-N".  Add new self-tests.  Drop
 "all" and "none" aliases as redundant and not worth the extra complication. ]

Cc: Li Zefan <lizefan@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

---

Paul Gortmaker (8):
  lib: test_bitmap: clearly separate ERANGE from EINVAL tests.
  lib: test_bitmap: add more start-end:offset/len tests
  lib: bitmap: fold nbits into region struct
  lib: bitmap: move ERANGE check from set_region to check_region
  lib: bitmap_getnum: separate arg into region and field
  lib: bitmap: support "N" as an alias for size of bitmap
  lib: test_bitmap: add tests for "N" alias
  rcu: deprecate "all" option to rcu_nocbs=

 .../admin-guide/kernel-parameters.rst         |  2 +
 .../admin-guide/kernel-parameters.txt         |  4 +-
 kernel/rcu/tree_plugin.h                      |  6 +--
 lib/bitmap.c                                  | 46 ++++++++++--------
 lib/test_bitmap.c                             | 48 ++++++++++++++++---
 5 files changed, 72 insertions(+), 34 deletions(-)

-- 
2.17.1

[PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Paul Gortmaker]

While this is done for all bitmaps, the original use case in mind was
for CPU masks and cpulist_parse() as described below.

It seems that a common configuration is to use the 1st couple cores for
housekeeping tasks.  This tends to leave the remaining ones to form a
pool of similarly configured cores to take on the real workload of
interest to the user.

So on machine A - with 32 cores, it could be 0-3 for "system" and then
4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
setting up the worker pool of CPUs.

But then newer machine B is added, and it has 48 cores, and so while
the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.

Multiple deployment becomes easier when we can just simply replace 31
and 47 with "N" and let the system substitute in the actual number at
boot; a number that it knows better than we do.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 Documentation/admin-guide/kernel-parameters.rst |  2 ++
 lib/bitmap.c                                    | 12 ++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index 682ab28b5c94..850917f19476 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -68,6 +68,8 @@ For example one can add to the command line following parameter:
 
 where the final item represents CPUs 100,101,125,126,150,151,...
 
+The value "N" can be used to represent the numerically last CPU on the system,
+i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
 
 
 This document may not be entirely up to date and comprehensive. The command
diff --git a/lib/bitmap.c b/lib/bitmap.c
index f65be2f148fd..2fdd00b312c3 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -519,11 +519,17 @@ static int bitmap_check_region(const struct region *r)
 	return 0;
 }
 
-static const char *bitmap_getnum(const char *str, unsigned int *num)
+static const char *__bitmap_getnum(const char *str, unsigned int nbits,
+				    unsigned int *num)
 {
 	unsigned long long n;
 	unsigned int len;
 
+	if (str[0] == 'N') {
+		*num = nbits - 1;
+		return str + 1;
+	}
+
 	len = _parse_integer(str, 10, &n);
 	if (!len)
 		return ERR_PTR(-EINVAL);
@@ -533,7 +539,7 @@ static const char *bitmap_getnum(const char *str, unsigned int *num)
 	*num = n;
 	return str + len;
 }
-#define bitmap_getrnum(s, r, pos) bitmap_getnum(s, &(r->pos))
+#define bitmap_getrnum(s, r, pos) __bitmap_getnum(s, r->nbits, &(r->pos))
 
 static inline bool end_of_str(char c)
 {
@@ -626,6 +632,8 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
  * From each group will be used only defined amount of bits.
  * Syntax: range:used_size/group_size
  * Example: 0-1023:2/256 ==> 0,1,256,257,512,513,768,769
+ * The value 'N' can be used as a dynamically substituted token for the
+ * maximum allowed value; i.e (nmaskbits - 1).
  *
  * Returns: 0 on success, -errno on invalid input strings. Error values:
  *
-- 
2.17.1

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Andy Shevchenko]

On Tue, Jan 26, 2021 at 12:11:39PM -0500, Paul Gortmaker wrote:
> While this is done for all bitmaps, the original use case in mind was
> for CPU masks and cpulist_parse() as described below.
> 
> It seems that a common configuration is to use the 1st couple cores for
> housekeeping tasks.  This tends to leave the remaining ones to form a
> pool of similarly configured cores to take on the real workload of
> interest to the user.
> 
> So on machine A - with 32 cores, it could be 0-3 for "system" and then
> 4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
> setting up the worker pool of CPUs.
> 
> But then newer machine B is added, and it has 48 cores, and so while
> the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.
> 
> Multiple deployment becomes easier when we can just simply replace 31
> and 47 with "N" and let the system substitute in the actual number at
> boot; a number that it knows better than we do.

I would accept lower 'n' as well.

...

> -static const char *bitmap_getnum(const char *str, unsigned int *num)
> +static const char *__bitmap_getnum(const char *str, unsigned int nbits,
> +				    unsigned int *num)
>  {
>  	unsigned long long n;
>  	unsigned int len;
>  
> +	if (str[0] == 'N') {
> +		*num = nbits - 1;
> +		return str + 1;
> +	}

But locating it here makes possible to enter a priori invalid input, like N for
start of the region.

I think this should be separate helper which is called in places where it makes
sense.

>  	len = _parse_integer(str, 10, &n);
>  	if (!len)
>  		return ERR_PTR(-EINVAL);


-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Andy Shevchenko]

On Tue, Jan 26, 2021 at 11:37:30PM +0200, Andy Shevchenko wrote:
> On Tue, Jan 26, 2021 at 12:11:39PM -0500, Paul Gortmaker wrote:

...

> > +	if (str[0] == 'N') {
> > +		*num = nbits - 1;
> > +		return str + 1;
> > +	}
> 
> But locating it here makes possible to enter a priori invalid input, like N for
> start of the region.
> 
> I think this should be separate helper which is called in places where it makes
> sense.

Okay, N is 31 on 32 core system... It is a bit counter intuitive, because it's
rather _L_ast than _N_umber of CPUs.

Changing letter?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Yury Norov]

On Tue, Jan 26, 2021 at 1:40 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Tue, Jan 26, 2021 at 11:37:30PM +0200, Andy Shevchenko wrote:
> > On Tue, Jan 26, 2021 at 12:11:39PM -0500, Paul Gortmaker wrote:
>
> ...
>
> > > +   if (str[0] == 'N') {
> > > +           *num = nbits - 1;
> > > +           return str + 1;
> > > +   }
> >
> > But locating it here makes possible to enter a priori invalid input, like N for
> > start of the region.
> >
> > I think this should be separate helper which is called in places where it makes
> > sense.
>
> Okay, N is 31 on 32 core system... It is a bit counter intuitive, because it's
> rather _L_ast than _N_umber of CPUs.
>
> Changing letter?

No objections.

Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap

[Paul Gortmaker]

[Re: [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap] On 26/01/2021 (Tue 23:37) Andy Shevchenko wrote:

> On Tue, Jan 26, 2021 at 12:11:39PM -0500, Paul Gortmaker wrote:
> > While this is done for all bitmaps, the original use case in mind was
> > for CPU masks and cpulist_parse() as described below.
> > 
> > It seems that a common configuration is to use the 1st couple cores for
> > housekeeping tasks.  This tends to leave the remaining ones to form a
> > pool of similarly configured cores to take on the real workload of
> > interest to the user.
> > 
> > So on machine A - with 32 cores, it could be 0-3 for "system" and then
> > 4-31 being used in boot args like nohz_full=, or rcu_nocbs= as part of
> > setting up the worker pool of CPUs.
> > 
> > But then newer machine B is added, and it has 48 cores, and so while
> > the 0-3 part remains unchanged, the pool setup cpu list becomes 4-47.
> > 
> > Multiple deployment becomes easier when we can just simply replace 31
> > and 47 with "N" and let the system substitute in the actual number at
> > boot; a number that it knows better than we do.
> 
> I would accept lower 'n' as well.
> 
> ...
> 
> > -static const char *bitmap_getnum(const char *str, unsigned int *num)
> > +static const char *__bitmap_getnum(const char *str, unsigned int nbits,
> > +				    unsigned int *num)
> >  {
> >  	unsigned long long n;
> >  	unsigned int len;
> >  
> > +	if (str[0] == 'N') {
> > +		*num = nbits - 1;
> > +		return str + 1;
> > +	}
> 
> But locating it here makes possible to enter a priori invalid input, like N for
> start of the region.

Actually, no.  N can be valid input for start of the region - or for any
field in the region.  I was originally thinking like you -- that N
was only valid as the end of the region, but Yury made a compelling
argument that N should be treated exactly as any other number is.

Skip down to where Yury says:
     So, when I do echo N-N > cpuset.cpus, I want it to work as
     if I do echo 15-15 > cpuset.cpus.

  https://lore.kernel.org/lkml/20210126171811.GC23530@windriver.com/

You weren't Cc'd at that point as I'd not added any self-test changes
to the series yet - so you didn't probably see that discussion.

This is why you'll see "N-N:N/N" added as a self-test that works.  It
doesn't make any more sense than using 15-15:15/15 does (vs. "15") but
both are equally valid inputs, in that they don't trigger an error.

Thanks,
Paul.
--

> 
> I think this should be separate helper which is called in places where it makes
> sense.
> 
> >  	len = _parse_integer(str, 10, &n);
> >  	if (!len)
> >  		return ERR_PTR(-EINVAL);
> 
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>