[PATCH tip/core/rcu 0/2] Add "all" to bitmap ranges

[PATCH tip/core/rcu 0/2] Add "all" to bitmap ranges

[Paul E. McKenney]

Hello!

This series adds "all" as a first-class bitmap range, for example so that
"rcu_nocbs=all:1/2" would offload all the even-numbered CPUs regardless
of the number of CPUs on the system.

1.	bitmap_parse: Support 'all' semantics, courtesy of Yury Norov.

2.	rcu/tree_plugin: Don't handle the case of 'all' CPU range,
	courtesy of Yury Norov.

						Thanx, Paul

------------------------------------------------------------------------

 Documentation/admin-guide/kernel-parameters.rst |    5 +++++
 kernel/rcu/tree_plugin.h                        |    9 +++------
 lib/bitmap.c                                    |    9 +++++++++
 lib/test_bitmap.c                               |    7 +++++++
 4 files changed, 24 insertions(+), 6 deletions(-)

[PATCH tip/core/rcu 1/2] bitmap_parse: Support 'all' semantics

[Paul E. McKenney]

From: Yury Norov <yury.norov@gmail.com>

RCU code supports an 'all' group as a special case when parsing rcu_nocbs
parameter. This patch moves the 'all' support to the core bitmap_parse
code, so that all bitmap users can enjoy this extension.

Moving 'all' parsing to a bitmap_parse level also allows users to pass
patterns together with 'all' in regular group:pattern format, for example,
"rcu_nocbs=all:1/2" would offload all the even-numbered CPUs regardless
of the number of CPUs on the system.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.rst | 5 +++++
 lib/bitmap.c                                    | 9 +++++++++
 lib/test_bitmap.c                               | 7 +++++++
 3 files changed, 21 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index 3996b54158bf..01ba293a2d70 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -76,6 +76,11 @@ 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).
 
+The special case-tolerant group name "all" has a meaning of selecting all CPUs,
+so that "nohz_full=all" is the equivalent of "nohz_full=0-N".
+
+The semantics of "N" and "all" is supported on a level of bitmaps and holds for
+all users of bitmap_parse().
 
 This document may not be entirely up to date and comprehensive. The command
 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 74ceb02f45e3..6e29b2aae6ba 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -581,6 +581,14 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
 {
 	unsigned int lastbit = r->nbits - 1;
 
+	if (!strncasecmp(str, "all", 3)) {
+		r->start = 0;
+		r->end = lastbit;
+		str += 3;
+
+		goto check_pattern;
+	}
+
 	str = bitmap_getnum(str, &r->start, lastbit);
 	if (IS_ERR(str))
 		return str;
@@ -595,6 +603,7 @@ static const char *bitmap_parse_region(const char *str, struct region *r)
 	if (IS_ERR(str))
 		return str;
 
+check_pattern:
 	if (end_of_region(*str))
 		goto no_pattern;
 
diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 9cd575583180..4ea73f5aed41 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -366,6 +366,13 @@ static const struct test_bitmap_parselist parselist_tests[] __initconst = {
 	{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},
 
+	{0,	  "all",		&exp1[8 * step], 32, 0},
+	{0,	  "0, 1, all,  ",	&exp1[8 * step], 32, 0},
+	{0,	  "all:1/2",		&exp1[4 * step], 32, 0},
+	{0,	  "ALL:1/2",		&exp1[4 * step], 32, 0},
+	{-EINVAL, "al", NULL, 8, 0},
+	{-EINVAL, "alll", NULL, 8, 0},
+
 	{-EINVAL, "-1",	NULL, 8, 0},
 	{-EINVAL, "-0",	NULL, 8, 0},
 	{-EINVAL, "10-1", NULL, 8, 0},
-- 
2.31.1.189.g2e36527f23

[PATCH tip/core/rcu 2/2] rcu/tree_plugin: Don't handle the case of 'all' CPU range

[Paul E. McKenney]

From: Yury Norov <yury.norov@gmail.com>

The 'all' semantics is now supported by the bitmap_parselist() so we can
drop supporting it as a special case in RCU code.  Since 'all' is properly
supported in core bitmap code, also drop legacy comment in RCU for it.

This patch does not make any functional changes for existing users.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_plugin.h | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index ad0156b86937..3f7a345b3814 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1535,13 +1535,10 @@ static void rcu_cleanup_after_idle(void)
 static int __init rcu_nocb_setup(char *str)
 {
 	alloc_bootmem_cpumask_var(&rcu_nocb_mask);
-	if (!strcasecmp(str, "all"))		/* legacy: use "0-N" instead */
+	if (cpulist_parse(str, rcu_nocb_mask)) {
+		pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
 		cpumask_setall(rcu_nocb_mask);
-	else
-		if (cpulist_parse(str, rcu_nocb_mask)) {
-			pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
-			cpumask_setall(rcu_nocb_mask);
-		}
+	}
 	return 1;
 }
 __setup("rcu_nocbs=", rcu_nocb_setup);
-- 
2.31.1.189.g2e36527f23