[PATCH] sched: Move sched_entity::avg into separate cache line

[PATCH] sched: Move sched_entity::avg into separate cache line

[Jiri Olsa]

From: root <root@hp-dl380gen9-01.khw.lab.eng.bos.redhat.com>

hi,
I tried Joe's and Don's c2c tool and it identified
a place with cache line contention. There're more
that poped up, this one was just too obvious ;-)

thanks
jirka


---
The sched_entity::avg collides with read-mostly sched_entity data.

The perf c2c tool showed many read HITM accesses across
many CPUs for sched_entity's cfs_rq and my_q, while having
at the same time tons of stores for avg.

After placing sched_entity::avg into separate cache line,
the perf bench sched pipe showed around 20 seconds speedup.

NOTE I cut out all perf events except for cycles and
instructions from following output.

Before:
  $ perf stat -r 5 perf bench sched pipe -l 10000000
  # Running 'sched/pipe' benchmark:
  # Executed 10000000 pipe operations between two processes

       Total time: 270.348 [sec]

        27.034805 usecs/op
            36989 ops/sec
   ...

     245,537,074,035      cycles                    #    1.433 GHz
     187,264,548,519      instructions              #    0.77  insns per cycle

       272.653840535 seconds time elapsed           ( +-  1.31% )

After:
  $ perf stat -r 5 perf bench sched pipe -l 10000000
  # Running 'sched/pipe' benchmark:
  # Executed 10000000 pipe operations between two processes

       Total time: 251.076 [sec]

        25.107678 usecs/op
            39828 ops/sec
  ...

     244,573,513,928      cycles                    #    1.572 GHz
     187,409,641,157      instructions              #    0.76  insns per cycle

       251.679315188 seconds time elapsed           ( +-  0.31% )

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/linux/sched.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3b0de68bce41..80cc1432e6e3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1268,8 +1268,13 @@ struct sched_entity {
 #endif
 
 #ifdef CONFIG_SMP
-	/* Per entity load average tracking */
-	struct sched_avg	avg;
+	/*
+	 * Per entity load average tracking.
+	 *
+	 * Put into separate cache line so it does not
+	 * collide with read-mostly values above.
+	 */
+	struct sched_avg	avg ____cacheline_aligned_in_smp;
 #endif
 };
 
-- 
2.4.3

Re: [PATCH] sched: Move sched_entity::avg into separate cache line

[Arnaldo Carvalho de Melo]

Em Tue, Dec 08, 2015 at 09:23:59PM +0100, Jiri Olsa escreveu:
> From: root <root@hp-dl380gen9-01.khw.lab.eng.bos.redhat.com>
> 
> hi,
> I tried Joe's and Don's c2c tool and it identified
> a place with cache line contention. There're more
> that poped up, this one was just too obvious ;-)

Would be interesting to see output from that tool and how you have
interpreted it to be for that specific data structure.

- Arnaldo
 
> thanks
> jirka
> 
> 
> ---
> The sched_entity::avg collides with read-mostly sched_entity data.
> 
> The perf c2c tool showed many read HITM accesses across
> many CPUs for sched_entity's cfs_rq and my_q, while having
> at the same time tons of stores for avg.
> 
> After placing sched_entity::avg into separate cache line,
> the perf bench sched pipe showed around 20 seconds speedup.
> 
> NOTE I cut out all perf events except for cycles and
> instructions from following output.
> 
> Before:
>   $ perf stat -r 5 perf bench sched pipe -l 10000000
>   # Running 'sched/pipe' benchmark:
>   # Executed 10000000 pipe operations between two processes
> 
>        Total time: 270.348 [sec]
> 
>         27.034805 usecs/op
>             36989 ops/sec
>    ...
> 
>      245,537,074,035      cycles                    #    1.433 GHz
>      187,264,548,519      instructions              #    0.77  insns per cycle
> 
>        272.653840535 seconds time elapsed           ( +-  1.31% )
> 
> After:
>   $ perf stat -r 5 perf bench sched pipe -l 10000000
>   # Running 'sched/pipe' benchmark:
>   # Executed 10000000 pipe operations between two processes
> 
>        Total time: 251.076 [sec]
> 
>         25.107678 usecs/op
>             39828 ops/sec
>   ...
> 
>      244,573,513,928      cycles                    #    1.572 GHz
>      187,409,641,157      instructions              #    0.76  insns per cycle
> 
>        251.679315188 seconds time elapsed           ( +-  0.31% )
> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  include/linux/sched.h | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 3b0de68bce41..80cc1432e6e3 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1268,8 +1268,13 @@ struct sched_entity {
>  #endif
>  
>  #ifdef CONFIG_SMP
> -	/* Per entity load average tracking */
> -	struct sched_avg	avg;
> +	/*
> +	 * Per entity load average tracking.
> +	 *
> +	 * Put into separate cache line so it does not
> +	 * collide with read-mostly values above.
> +	 */
> +	struct sched_avg	avg ____cacheline_aligned_in_smp;
>  #endif
>  };
>  
> -- 
> 2.4.3

[tip:sched/core] sched/core: Move sched_entity:: avg into separate cache line

[tip-bot for Jiri Olsa]

Commit-ID:  5a1078043f844074cbd53981432778a8d5dd56e9
Gitweb:     http://git.kernel.org/tip/5a1078043f844074cbd53981432778a8d5dd56e9
Author:     Jiri Olsa <jolsa@kernel.org>
AuthorDate: Tue, 8 Dec 2015 21:23:59 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 6 Jan 2016 11:06:14 +0100

sched/core: Move sched_entity::avg into separate cache line

The sched_entity::avg collides with read-mostly sched_entity data.

The perf c2c tool showed many read HITM accesses across
many CPUs for sched_entity's cfs_rq and my_q, while having
at the same time tons of stores for avg.

After placing sched_entity::avg into separate cache line,
the perf bench sched pipe showed around 20 seconds speedup.

NOTE I cut out all perf events except for cycles and
instructions from following output.

Before:
  $ perf stat -r 5 perf bench sched pipe -l 10000000
  # Running 'sched/pipe' benchmark:
  # Executed 10000000 pipe operations between two processes

       Total time: 270.348 [sec]

        27.034805 usecs/op
            36989 ops/sec
   ...

     245,537,074,035      cycles                    #    1.433 GHz
     187,264,548,519      instructions              #    0.77  insns per cycle

       272.653840535 seconds time elapsed           ( +-  1.31% )

After:
  $ perf stat -r 5 perf bench sched pipe -l 10000000
  # Running 'sched/pipe' benchmark:
  # Executed 10000000 pipe operations between two processes

       Total time: 251.076 [sec]

        25.107678 usecs/op
            39828 ops/sec
  ...

     244,573,513,928      cycles                    #    1.572 GHz
     187,409,641,157      instructions              #    0.76  insns per cycle

       251.679315188 seconds time elapsed           ( +-  0.31% )

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Joe Mario <jmario@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1449606239-28602-1-git-send-email-jolsa@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/sched.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 791b47e..0c0e781 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1268,8 +1268,13 @@ struct sched_entity {
 #endif
 
 #ifdef CONFIG_SMP
-	/* Per entity load average tracking */
-	struct sched_avg	avg;
+	/*
+	 * Per entity load average tracking.
+	 *
+	 * Put into separate cache line so it does not
+	 * collide with read-mostly values above.
+	 */
+	struct sched_avg	avg ____cacheline_aligned_in_smp;
 #endif
 };