[PATCH 0/2] small scheduler debug stat fixups

[PATCH 0/2] small scheduler debug stat fixups

[Joe Lawrence]

A customer noticed some misalignment issues in the scheduler debug stats
caused by line break/continuations.  While the kernel isn't responsible
for log rendering, these trivial changes can help clean up the stats
display with default settings for dmesg/rsyslog/etc.  

Note that /proc/sched_debug didn't suffer from these issues and its
output remains unchanged by this patchset.

Joe Lawrence (2):
  sched/debug: fix per-task line continuation for console
  sched/debug: adjust newlines for better alignment

 kernel/sched/debug.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

-- 
1.8.3.1

[PATCH 1/2] sched/debug: fix per-task line continuation for console

[Joe Lawrence]

When the SEQ_printf() macro prints to the console, it runs a simple
printk() without KERN_CONT "continued" line printing.  The result of
this is oddly wrapped task info, for example:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  runnable tasks:
  ...
  [   29.608611]  I
  [   29.608613]       rcu_sched     8      3252.013846      4087   120
  [   29.608614]         0.000000        29.090111         0.000000
  [   29.608615]  0 0
  [   29.608616]  /

Modify SEQ_printf to use pr_cont() for expected one-line results:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  runnable tasks:
  ...
  [  106.716329]  S        cpuhp/5    37      2006.315026        14   120         0.000000         0.496893         0.000000 0 0 /

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 1ca0130ed4f9..50026aa2d81e 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -32,7 +32,7 @@
 	if (m)					\
 		seq_printf(m, x);		\
 	else					\
-		printk(x);			\
+		pr_cont(x);			\
  } while (0)
 
 /*
-- 
1.8.3.1

Re: [PATCH 1/2] sched/debug: fix per-task line continuation for console

[Peter Zijlstra]

On Mon, Mar 19, 2018 at 02:35:54PM -0400, Joe Lawrence wrote:
> When the SEQ_printf() macro prints to the console, it runs a simple
> printk() without KERN_CONT "continued" line printing.  The result of
> this is oddly wrapped task info, for example:
> 
>   % echo t > /proc/sysrq-trigger
>   % dmesg
>   ...
>   runnable tasks:
>   ...
>   [   29.608611]  I
>   [   29.608613]       rcu_sched     8      3252.013846      4087   120
>   [   29.608614]         0.000000        29.090111         0.000000
>   [   29.608615]  0 0
>   [   29.608616]  /
> 
> Modify SEQ_printf to use pr_cont() for expected one-line results:
> 
>   % echo t > /proc/sysrq-trigger
>   % dmesg
>   ...
>   runnable tasks:
>   ...
>   [  106.716329]  S        cpuhp/5    37      2006.315026        14   120         0.000000         0.496893         0.000000 0 0 /
> 
> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
> ---
>  kernel/sched/debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 1ca0130ed4f9..50026aa2d81e 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -32,7 +32,7 @@
>  	if (m)					\
>  		seq_printf(m, x);		\
>  	else					\
> -		printk(x);			\
> +		pr_cont(x);			\

That used to work I think.. I think someone changed how printk() behaves
somewhere along the lines.

Does pr_cont("\n") DTRT? it seems like something weird.

Re: [PATCH 1/2] sched/debug: fix per-task line continuation for console

[Joe Lawrence]

On 03/19/2018 04:17 PM, Peter Zijlstra wrote:
> On Mon, Mar 19, 2018 at 02:35:54PM -0400, Joe Lawrence wrote:
>> When the SEQ_printf() macro prints to the console, it runs a simple
>> printk() without KERN_CONT "continued" line printing.  The result of
>> this is oddly wrapped task info, for example:
>>
>>   % echo t > /proc/sysrq-trigger
>>   % dmesg
>>   ...
>>   runnable tasks:
>>   ...
>>   [   29.608611]  I
>>   [   29.608613]       rcu_sched     8      3252.013846      4087   120
>>   [   29.608614]         0.000000        29.090111         0.000000
>>   [   29.608615]  0 0
>>   [   29.608616]  /
>>
>> Modify SEQ_printf to use pr_cont() for expected one-line results:
>>
>>   % echo t > /proc/sysrq-trigger
>>   % dmesg
>>   ...
>>   runnable tasks:
>>   ...
>>   [  106.716329]  S        cpuhp/5    37      2006.315026        14   120         0.000000         0.496893         0.000000 0 0 /
>>
>> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
>> ---
>>  kernel/sched/debug.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
>> index 1ca0130ed4f9..50026aa2d81e 100644
>> --- a/kernel/sched/debug.c
>> +++ b/kernel/sched/debug.c
>> @@ -32,7 +32,7 @@
>>  	if (m)					\
>>  		seq_printf(m, x);		\
>>  	else					\
>> -		printk(x);			\
>> +		pr_cont(x);			\
> 
> That used to work I think.. I think someone changed how printk() behaves
> somewhere along the lines.
> 

Hi Peter,

This code:

        printk("printk one");
        printk("printk two\n");

        pr_cont("\n");
        pr_cont("pr_cont one");
        pr_cont("pr_cont two\n");

        pr_cont("pr_cont first line\n");
        pr_cont("\n");
        pr_cont("\n");
        pr_cont("pr_cont next line");

Creates this output:

	%  uname -r
	4.16.0-rc5+

	% dmesg
	[  575.221280] printk one
	[  575.221281] printk two
	[  575.221282] pr_cont onepr_cont two
	[  575.221283] pr_cont first line

I don't have the commit offhand that changed the printk behavior, but
from observation:

  1 - printk implies a trailing newline:
      https://lwn.net/Articles/732420/

  2 - pr_cont seems to eat redundant newlines

> Does pr_cont("\n") DTRT? it seems like something weird.
> 

Yeah, pr_cont() is kind of a hack.  It will terminate a line if that's
the first newline, but as demonstrated above, I don't think it likes
extra newline chars.

A better fix would be to marshal the text into temp buffer then dump it
out.  Dunno if you prefer that kind of churn for these stats.

-- Joe

Re: [PATCH 1/2] sched/debug: fix per-task line continuation for console

[Peter Zijlstra]

On Mon, Mar 19, 2018 at 04:43:28PM -0400, Joe Lawrence wrote:
> On 03/19/2018 04:17 PM, Peter Zijlstra wrote:

> I don't have the commit offhand that changed the printk behavior, but
> from observation:

4bcc595ccd80 ("printk: reinstate KERN_CONT for printing continuation lines")

and thereabout I think.

> > Does pr_cont("\n") DTRT? it seems like something weird.
> > 
> 
> Yeah, pr_cont() is kind of a hack.  It will terminate a line if that's
> the first newline, but as demonstrated above, I don't think it likes
> extra newline chars.

Fair enough I suppose, just a bit weird.

> A better fix would be to marshal the text into temp buffer then dump it
> out.  Dunno if you prefer that kind of churn for these stats.

Yeah, not worth it, simple is better here.

[tip:sched/urgent] sched/debug: Fix per-task line continuation for console output

[tip-bot for Joe Lawrence]

Commit-ID:  a8c024cd9b9683d25ae1f459525dd2c6bec75e79
Gitweb:     https://git.kernel.org/tip/a8c024cd9b9683d25ae1f459525dd2c6bec75e79
Author:     Joe Lawrence <joe.lawrence@redhat.com>
AuthorDate: Mon, 19 Mar 2018 14:35:54 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Mar 2018 09:30:09 +0100

sched/debug: Fix per-task line continuation for console output

When the SEQ_printf() macro prints to the console, it runs a simple
printk() without KERN_CONT "continued" line printing.  The result of
this is oddly wrapped task info, for example:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  runnable tasks:
  ...
  [   29.608611]  I
  [   29.608613]       rcu_sched     8      3252.013846      4087   120
  [   29.608614]         0.000000        29.090111         0.000000
  [   29.608615]  0 0
  [   29.608616]  /

Modify SEQ_printf to use pr_cont() for expected one-line results:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  runnable tasks:
  ...
  [  106.716329]  S        cpuhp/5    37      2006.315026        14   120         0.000000         0.496893         0.000000 0 0 /

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1521484555-8620-2-git-send-email-joe.lawrence@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 1ca0130ed4f9..50026aa2d81e 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -32,7 +32,7 @@ static DEFINE_SPINLOCK(sched_debug_lock);
 	if (m)					\
 		seq_printf(m, x);		\
 	else					\
-		printk(x);			\
+		pr_cont(x);			\
  } while (0)
 
 /*

[PATCH 2/2] sched/debug: adjust newlines for better alignment

[Joe Lawrence]

Scheduler debug stats include newlines that display out of alignment
when prefixed by timestamps.  For example, the dmesg utility:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  [   83.124251]
  runnable tasks:
   S           task   PID         tree-key  switches  prio     wait-time
  sum-exec        sum-sleep
  -----------------------------------------------------------------------------------------------------------

At the same time, some syslog utilities (like rsyslog by default) don't
like the additional newlines control characters, saving lines like this
to /var/log/messages:

  Mar 16 16:02:29 localhost kernel: #012runnable tasks:#012 S           task   PID         tree-key ...
                                    ^^^^               ^^^^
Clean these up by moving newline characters to their own SEQ_printf
invocation.  This leaves the /proc/sched_debug unchanged, but brings the
entire output into alignment when prefixed:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  [   62.410368] runnable tasks:
  [   62.410368]  S           task   PID         tree-key  switches  prio     wait-time             sum-exec        sum-sleep
  [   62.410369] -----------------------------------------------------------------------------------------------------------
  [   62.410369]  I  kworker/u12:0     5      1932.215593       332   120         0.000000         3.621252         0.000000 0 0 /

and no escaped control characters from rsyslog in /var/log/messages:

  Mar 16 16:15:06 localhost kernel: runnable tasks:
  Mar 16 16:15:06 localhost kernel: S           task   PID         tree-key  ...

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
 kernel/sched/debug.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 50026aa2d81e..72c401b3b15c 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -501,12 +501,12 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 {
 	struct task_struct *g, *p;
 
-	SEQ_printf(m,
-	"\nrunnable tasks:\n"
-	" S           task   PID         tree-key  switches  prio"
-	"     wait-time             sum-exec        sum-sleep\n"
-	"-------------------------------------------------------"
-	"----------------------------------------------------\n");
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "runnable tasks:\n");
+	SEQ_printf(m, " S           task   PID         tree-key  switches  prio"
+		   "     wait-time             sum-exec        sum-sleep\n");
+	SEQ_printf(m, "-------------------------------------------------------"
+		   "----------------------------------------------------\n");
 
 	rcu_read_lock();
 	for_each_process_thread(g, p) {
@@ -527,9 +527,11 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 	unsigned long flags;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-	SEQ_printf(m, "\ncfs_rq[%d]:%s\n", cpu, task_group_path(cfs_rq->tg));
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "cfs_rq[%d]:%s\n", cpu, task_group_path(cfs_rq->tg));
 #else
-	SEQ_printf(m, "\ncfs_rq[%d]:\n", cpu);
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "cfs_rq[%d]:\n", cpu);
 #endif
 	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "exec_clock",
 			SPLIT_NS(cfs_rq->exec_clock));
@@ -595,9 +597,11 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq)
 {
 #ifdef CONFIG_RT_GROUP_SCHED
-	SEQ_printf(m, "\nrt_rq[%d]:%s\n", cpu, task_group_path(rt_rq->tg));
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "rt_rq[%d]:%s\n", cpu, task_group_path(rt_rq->tg));
 #else
-	SEQ_printf(m, "\nrt_rq[%d]:\n", cpu);
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "rt_rq[%d]:\n", cpu);
 #endif
 
 #define P(x) \
@@ -624,7 +628,8 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq)
 {
 	struct dl_bw *dl_bw;
 
-	SEQ_printf(m, "\ndl_rq[%d]:\n", cpu);
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "dl_rq[%d]:\n", cpu);
 
 #define PU(x) \
 	SEQ_printf(m, "  .%-30s: %lu\n", #x, (unsigned long)(dl_rq->x))
-- 
1.8.3.1

[tip:sched/urgent] sched/debug: Adjust newlines for better alignment

[tip-bot for Joe Lawrence]

Commit-ID:  e9ca267096674eadd1fd479279bcb58df1486049
Gitweb:     https://git.kernel.org/tip/e9ca267096674eadd1fd479279bcb58df1486049
Author:     Joe Lawrence <joe.lawrence@redhat.com>
AuthorDate: Mon, 19 Mar 2018 14:35:55 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 20 Mar 2018 09:30:09 +0100

sched/debug: Adjust newlines for better alignment

Scheduler debug stats include newlines that display out of alignment
when prefixed by timestamps.  For example, the dmesg utility:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  [   83.124251]
  runnable tasks:
   S           task   PID         tree-key  switches  prio     wait-time
  sum-exec        sum-sleep
  -----------------------------------------------------------------------------------------------------------

At the same time, some syslog utilities (like rsyslog by default) don't
like the additional newlines control characters, saving lines like this
to /var/log/messages:

  Mar 16 16:02:29 localhost kernel: #012runnable tasks:#012 S           task   PID         tree-key ...
                                    ^^^^               ^^^^
Clean these up by moving newline characters to their own SEQ_printf
invocation.  This leaves the /proc/sched_debug unchanged, but brings the
entire output into alignment when prefixed:

  % echo t > /proc/sysrq-trigger
  % dmesg
  ...
  [   62.410368] runnable tasks:
  [   62.410368]  S           task   PID         tree-key  switches  prio     wait-time             sum-exec        sum-sleep
  [   62.410369] -----------------------------------------------------------------------------------------------------------
  [   62.410369]  I  kworker/u12:0     5      1932.215593       332   120         0.000000         3.621252         0.000000 0 0 /

and no escaped control characters from rsyslog in /var/log/messages:

  Mar 16 16:15:06 localhost kernel: runnable tasks:
  Mar 16 16:15:06 localhost kernel: S           task   PID         tree-key  ...

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1521484555-8620-3-git-send-email-joe.lawrence@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/debug.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 50026aa2d81e..72c401b3b15c 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -501,12 +501,12 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 {
 	struct task_struct *g, *p;
 
-	SEQ_printf(m,
-	"\nrunnable tasks:\n"
-	" S           task   PID         tree-key  switches  prio"
-	"     wait-time             sum-exec        sum-sleep\n"
-	"-------------------------------------------------------"
-	"----------------------------------------------------\n");
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "runnable tasks:\n");
+	SEQ_printf(m, " S           task   PID         tree-key  switches  prio"
+		   "     wait-time             sum-exec        sum-sleep\n");
+	SEQ_printf(m, "-------------------------------------------------------"
+		   "----------------------------------------------------\n");
 
 	rcu_read_lock();
 	for_each_process_thread(g, p) {
@@ -527,9 +527,11 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 	unsigned long flags;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-	SEQ_printf(m, "\ncfs_rq[%d]:%s\n", cpu, task_group_path(cfs_rq->tg));
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "cfs_rq[%d]:%s\n", cpu, task_group_path(cfs_rq->tg));
 #else
-	SEQ_printf(m, "\ncfs_rq[%d]:\n", cpu);
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "cfs_rq[%d]:\n", cpu);
 #endif
 	SEQ_printf(m, "  .%-30s: %Ld.%06ld\n", "exec_clock",
 			SPLIT_NS(cfs_rq->exec_clock));
@@ -595,9 +597,11 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq)
 {
 #ifdef CONFIG_RT_GROUP_SCHED
-	SEQ_printf(m, "\nrt_rq[%d]:%s\n", cpu, task_group_path(rt_rq->tg));
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "rt_rq[%d]:%s\n", cpu, task_group_path(rt_rq->tg));
 #else
-	SEQ_printf(m, "\nrt_rq[%d]:\n", cpu);
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "rt_rq[%d]:\n", cpu);
 #endif
 
 #define P(x) \
@@ -624,7 +628,8 @@ void print_dl_rq(struct seq_file *m, int cpu, struct dl_rq *dl_rq)
 {
 	struct dl_bw *dl_bw;
 
-	SEQ_printf(m, "\ndl_rq[%d]:\n", cpu);
+	SEQ_printf(m, "\n");
+	SEQ_printf(m, "dl_rq[%d]:\n", cpu);
 
 #define PU(x) \
 	SEQ_printf(m, "  .%-30s: %lu\n", #x, (unsigned long)(dl_rq->x))