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* [PATCH] sched: task_struct: Fill unconditional hole induced by sched_entity
@ 2021-09-24  2:54 Kees Cook
  2021-10-06  4:48 ` Kees Cook
  0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2021-09-24  2:54 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Kees Cook, Ingo Molnar, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	Daniel Bristot de Oliveira, linux-kernel, linux-hardening

With struct sched_entity before the other sched entities, its alignment
won't induce a struct hole. This saves 64 bytes in defconfig task_struct:

Before:
	...
        unsigned int               rt_priority;          /*   120     4 */

        /* XXX 4 bytes hole, try to pack */

        /* --- cacheline 2 boundary (128 bytes) --- */
        const struct sched_class  * sched_class;         /*   128     8 */

        /* XXX 56 bytes hole, try to pack */

        /* --- cacheline 3 boundary (192 bytes) --- */
        struct sched_entity        se __attribute__((__aligned__(64))); /*   192   448 */
        /* --- cacheline 10 boundary (640 bytes) --- */
        struct sched_rt_entity     rt;                   /*   640    48 */
        struct sched_dl_entity     dl __attribute__((__aligned__(8))); /*   688   224 */
        /* --- cacheline 14 boundary (896 bytes) was 16 bytes ago --- */

After:
	...
        unsigned int               rt_priority;          /*   120     4 */

        /* XXX 4 bytes hole, try to pack */

        /* --- cacheline 2 boundary (128 bytes) --- */
        struct sched_entity        se __attribute__((__aligned__(64))); /*   128   448 */
        /* --- cacheline 9 boundary (576 bytes) --- */
        struct sched_rt_entity     rt;                   /*   576    48 */
        struct sched_dl_entity     dl __attribute__((__aligned__(8))); /*   624   224 */
        /* --- cacheline 13 boundary (832 bytes) was 16 bytes ago --- */

Summary diff:
-	/* size: 7040, cachelines: 110, members: 188 */
+	/* size: 6976, cachelines: 109, members: 188 */

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/sched.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 39039ce8ac4c..27ed1d40028f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -775,10 +775,10 @@ struct task_struct {
 	int				normal_prio;
 	unsigned int			rt_priority;
 
-	const struct sched_class	*sched_class;
 	struct sched_entity		se;
 	struct sched_rt_entity		rt;
 	struct sched_dl_entity		dl;
+	const struct sched_class	*sched_class;
 
 #ifdef CONFIG_SCHED_CORE
 	struct rb_node			core_node;
-- 
2.30.2


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] sched: task_struct: Fill unconditional hole induced by sched_entity
  2021-09-24  2:54 [PATCH] sched: task_struct: Fill unconditional hole induced by sched_entity Kees Cook
@ 2021-10-06  4:48 ` Kees Cook
  2021-10-06  9:27   ` Peter Zijlstra
  0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2021-10-06  4:48 UTC (permalink / raw)
  To: Peter Zijlstra, Ingo Molnar, Thomas Gleixner, Borislav Petkov
  Cc: x86, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
	Steven Rostedt, Ben Segall, Mel Gorman,
	Daniel Bristot de Oliveira, linux-kernel, linux-hardening

On Thu, Sep 23, 2021 at 07:54:50PM -0700, Kees Cook wrote:
> With struct sched_entity before the other sched entities, its alignment
> won't induce a struct hole. This saves 64 bytes in defconfig task_struct:

Friendly ping. Can someone snag this for -tip please?

Thanks!

-Kees

> 
> Before:
> 	...
>         unsigned int               rt_priority;          /*   120     4 */
> 
>         /* XXX 4 bytes hole, try to pack */
> 
>         /* --- cacheline 2 boundary (128 bytes) --- */
>         const struct sched_class  * sched_class;         /*   128     8 */
> 
>         /* XXX 56 bytes hole, try to pack */
> 
>         /* --- cacheline 3 boundary (192 bytes) --- */
>         struct sched_entity        se __attribute__((__aligned__(64))); /*   192   448 */
>         /* --- cacheline 10 boundary (640 bytes) --- */
>         struct sched_rt_entity     rt;                   /*   640    48 */
>         struct sched_dl_entity     dl __attribute__((__aligned__(8))); /*   688   224 */
>         /* --- cacheline 14 boundary (896 bytes) was 16 bytes ago --- */
> 
> After:
> 	...
>         unsigned int               rt_priority;          /*   120     4 */
> 
>         /* XXX 4 bytes hole, try to pack */
> 
>         /* --- cacheline 2 boundary (128 bytes) --- */
>         struct sched_entity        se __attribute__((__aligned__(64))); /*   128   448 */
>         /* --- cacheline 9 boundary (576 bytes) --- */
>         struct sched_rt_entity     rt;                   /*   576    48 */
>         struct sched_dl_entity     dl __attribute__((__aligned__(8))); /*   624   224 */
>         /* --- cacheline 13 boundary (832 bytes) was 16 bytes ago --- */
> 
> Summary diff:
> -	/* size: 7040, cachelines: 110, members: 188 */
> +	/* size: 6976, cachelines: 109, members: 188 */
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  include/linux/sched.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 39039ce8ac4c..27ed1d40028f 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -775,10 +775,10 @@ struct task_struct {
>  	int				normal_prio;
>  	unsigned int			rt_priority;
>  
> -	const struct sched_class	*sched_class;
>  	struct sched_entity		se;
>  	struct sched_rt_entity		rt;
>  	struct sched_dl_entity		dl;
> +	const struct sched_class	*sched_class;
>  
>  #ifdef CONFIG_SCHED_CORE
>  	struct rb_node			core_node;
> -- 
> 2.30.2
> 

-- 
Kees Cook

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] sched: task_struct: Fill unconditional hole induced by sched_entity
  2021-10-06  4:48 ` Kees Cook
@ 2021-10-06  9:27   ` Peter Zijlstra
  2021-10-06 16:31     ` Kees Cook
  0 siblings, 1 reply; 4+ messages in thread
From: Peter Zijlstra @ 2021-10-06  9:27 UTC (permalink / raw)
  To: Kees Cook
  Cc: Ingo Molnar, Thomas Gleixner, Borislav Petkov, x86, Juri Lelli,
	Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
	Mel Gorman, Daniel Bristot de Oliveira, linux-kernel,
	linux-hardening

On Tue, Oct 05, 2021 at 09:48:51PM -0700, Kees Cook wrote:
> On Thu, Sep 23, 2021 at 07:54:50PM -0700, Kees Cook wrote:
> > With struct sched_entity before the other sched entities, its alignment
> > won't induce a struct hole. This saves 64 bytes in defconfig task_struct:
> 
> Friendly ping. Can someone snag this for -tip please?

Hurpmf... if only we had like perf driven pahole output :/

Picked it up, we'll see what if anything hurts.

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] sched: task_struct: Fill unconditional hole induced by sched_entity
  2021-10-06  9:27   ` Peter Zijlstra
@ 2021-10-06 16:31     ` Kees Cook
  0 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2021-10-06 16:31 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Ingo Molnar, Thomas Gleixner, Borislav Petkov, x86, Juri Lelli,
	Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
	Mel Gorman, Daniel Bristot de Oliveira, linux-kernel,
	linux-hardening

On Wed, Oct 06, 2021 at 11:27:03AM +0200, Peter Zijlstra wrote:
> On Tue, Oct 05, 2021 at 09:48:51PM -0700, Kees Cook wrote:
> > On Thu, Sep 23, 2021 at 07:54:50PM -0700, Kees Cook wrote:
> > > With struct sched_entity before the other sched entities, its alignment
> > > won't induce a struct hole. This saves 64 bytes in defconfig task_struct:
> > 
> > Friendly ping. Can someone snag this for -tip please?
> 
> Hurpmf... if only we had like perf driven pahole output :/

Normally I wouldn't even make suggestions in task_struct given the high
variability due to CONFIG options, but this case was pretty universal.

> Picked it up, we'll see what if anything hurts.

Thanks! *fingers crossed*

-- 
Kees Cook

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-10-06 16:31 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-09-24  2:54 [PATCH] sched: task_struct: Fill unconditional hole induced by sched_entity Kees Cook
2021-10-06  4:48 ` Kees Cook
2021-10-06  9:27   ` Peter Zijlstra
2021-10-06 16:31     ` Kees Cook

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