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* [PATCH] sched/fair: ignore cache hotness for SMT migration
@ 2020-08-04  0:06 Josh Don
  2020-08-04 10:56 ` peterz
  0 siblings, 1 reply; 7+ messages in thread
From: Josh Don @ 2020-08-04  0:06 UTC (permalink / raw)
  To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot
  Cc: Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	linux-kernel, Josh Don

SMT siblings share caches, so cache hotness should be irrelevant for
cross-sibling migration.

Proposed-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Josh Don <joshdon@google.com>
---
 kernel/sched/fair.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2ba8f230feb9..5b203b55bcb2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7402,6 +7402,9 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 	if (unlikely(task_has_idle_policy(p)))
 		return 0;
 
+	if ((env->sd->flags & cpu_smt_flags()) == cpu_smt_flags())
+		return 0;
+
 	/*
 	 * Buddy candidates are cache hot:
 	 */
-- 
2.28.0.163.g6104cc2f0b6-goog


^ permalink raw reply related	[flat|nested] 7+ messages in thread
* Re: [PATCH] sched/fair: ignore cache hotness for SMT migration
  2020-08-04  0:06 [PATCH] sched/fair: ignore cache hotness for SMT migration Josh Don
@ 2020-08-04 10:56 ` peterz
  2020-08-04 19:24   ` Josh Don
  2020-08-04 19:34   ` [PATCH v2] " Josh Don
  0 siblings, 2 replies; 7+ messages in thread
From: peterz @ 2020-08-04 10:56 UTC (permalink / raw)
  To: Josh Don
  Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
	Steven Rostedt, Ben Segall, Mel Gorman, linux-kernel

On Mon, Aug 03, 2020 at 05:06:14PM -0700, Josh Don wrote:
> SMT siblings share caches, so cache hotness should be irrelevant for
> cross-sibling migration.
> 
> Proposed-by: Venkatesh Pallipadi <venki@google.com>
> Signed-off-by: Josh Don <joshdon@google.com>
> ---
>  kernel/sched/fair.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 2ba8f230feb9..5b203b55bcb2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7402,6 +7402,9 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
>  	if (unlikely(task_has_idle_policy(p)))
>  		return 0;
>  
> +	if ((env->sd->flags & cpu_smt_flags()) == cpu_smt_flags())
> +		return 0;

I think that wants to be:

	if (env->sd->flags & SD_SHARE_CPUCAPACITY)

Also, perhaps stick a comment on top with the rationale for this.

> +
>  	/*
>  	 * Buddy candidates are cache hot:
>  	 */
> -- 
> 2.28.0.163.g6104cc2f0b6-goog
> 

^ permalink raw reply	[flat|nested] 7+ messages in thread
* Re: [PATCH] sched/fair: ignore cache hotness for SMT migration
  2020-08-04 10:56 ` peterz
@ 2020-08-04 19:24   ` Josh Don
  2020-08-04 19:34   ` [PATCH v2] " Josh Don
  1 sibling, 0 replies; 7+ messages in thread
From: Josh Don @ 2020-08-04 19:24 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
	Steven Rostedt, Ben Segall, Mel Gorman, linux-kernel

On Tue, Aug 4, 2020 at 3:56 AM <peterz@infradead.org> wrote:
>
> On Mon, Aug 03, 2020 at 05:06:14PM -0700, Josh Don wrote:
> > SMT siblings share caches, so cache hotness should be irrelevant for
> > cross-sibling migration.
> >
> > Proposed-by: Venkatesh Pallipadi <venki@google.com>
> > Signed-off-by: Josh Don <joshdon@google.com>
> > ---
> >  kernel/sched/fair.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 2ba8f230feb9..5b203b55bcb2 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7402,6 +7402,9 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
> >       if (unlikely(task_has_idle_policy(p)))
> >               return 0;
> >
> > +     if ((env->sd->flags & cpu_smt_flags()) == cpu_smt_flags())
> > +             return 0;
>
> I think that wants to be:
>
>         if (env->sd->flags & SD_SHARE_CPUCAPACITY)
>

Agreed

> Also, perhaps stick a comment on top with the rationale for this.
>
> > +
> >       /*
> >        * Buddy candidates are cache hot:
> >        */
> > --
> > 2.28.0.163.g6104cc2f0b6-goog
> >

^ permalink raw reply	[flat|nested] 7+ messages in thread
* [PATCH v2] sched/fair: ignore cache hotness for SMT migration
  2020-08-04 10:56 ` peterz
  2020-08-04 19:24   ` Josh Don
@ 2020-08-04 19:34   ` Josh Don
  2020-08-10  6:14     ` Srikar Dronamraju
  2020-08-27  7:54     ` [tip: sched/core] sched/fair: Ignore " tip-bot2 for Josh Don
  1 sibling, 2 replies; 7+ messages in thread
From: Josh Don @ 2020-08-04 19:34 UTC (permalink / raw)
  To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot
  Cc: Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	linux-kernel, Josh Don

SMT siblings share caches, so cache hotness should be irrelevant for
cross-sibling migration.

Proposed-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Josh Don <joshdon@google.com>
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1a68a0536add..abdb54e2339f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7402,6 +7402,10 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 	if (unlikely(task_has_idle_policy(p)))
 		return 0;
 
+	/* SMT siblings share cache */
+	if (env->sd->flags & SD_SHARE_CPUCAPACITY)
+		return 0;
+
 	/*
 	 * Buddy candidates are cache hot:
 	 */
-- 
2.28.0.163.g6104cc2f0b6-goog


^ permalink raw reply related	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] sched/fair: ignore cache hotness for SMT migration
  2020-08-04 19:34   ` [PATCH v2] " Josh Don
@ 2020-08-10  6:14     ` Srikar Dronamraju
  2020-08-10  8:55       ` Valentin Schneider
  2020-08-27  7:54     ` [tip: sched/core] sched/fair: Ignore " tip-bot2 for Josh Don
  1 sibling, 1 reply; 7+ messages in thread
From: Srikar Dronamraju @ 2020-08-10  6:14 UTC (permalink / raw)
  To: Josh Don
  Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
	Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
	linux-kernel

* Josh Don <joshdon@google.com> [2020-08-04 12:34:13]:

> SMT siblings share caches, so cache hotness should be irrelevant for
> cross-sibling migration.
> 
> Proposed-by: Venkatesh Pallipadi <venki@google.com>
> Signed-off-by: Josh Don <joshdon@google.com>
> ---
>  kernel/sched/fair.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a0536add..abdb54e2339f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7402,6 +7402,10 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
>  	if (unlikely(task_has_idle_policy(p)))
>  		return 0;
>  
> +	/* SMT siblings share cache */
> +	if (env->sd->flags & SD_SHARE_CPUCAPACITY)
> +		return 0;
> +

If this for retaining cache hotness, should we look at
SD_SHARE_PKG_RESOURCES instead of SD_SHARE_CPUCAPACITY?

>  	/*
>  	 * Buddy candidates are cache hot:
>  	 */
> -- 
> 2.28.0.163.g6104cc2f0b6-goog
> 

-- 
Thanks and Regards
Srikar Dronamraju

^ permalink raw reply	[flat|nested] 7+ messages in thread
* Re: [PATCH v2] sched/fair: ignore cache hotness for SMT migration
  2020-08-10  6:14     ` Srikar Dronamraju
@ 2020-08-10  8:55       ` Valentin Schneider
  0 siblings, 0 replies; 7+ messages in thread
From: Valentin Schneider @ 2020-08-10  8:55 UTC (permalink / raw)
  To: Srikar Dronamraju
  Cc: Josh Don, Ingo Molnar, Peter Zijlstra, Juri Lelli,
	Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
	Mel Gorman, linux-kernel


On 10/08/20 07:14, Srikar Dronamraju wrote:
> * Josh Don <joshdon@google.com> [2020-08-04 12:34:13]:
>
>> SMT siblings share caches, so cache hotness should be irrelevant for
>> cross-sibling migration.
>>
>> Proposed-by: Venkatesh Pallipadi <venki@google.com>
>> Signed-off-by: Josh Don <joshdon@google.com>
>> ---
>>  kernel/sched/fair.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 1a68a0536add..abdb54e2339f 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -7402,6 +7402,10 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
>>      if (unlikely(task_has_idle_policy(p)))
>>              return 0;
>>
>> +	/* SMT siblings share cache */
>> +	if (env->sd->flags & SD_SHARE_CPUCAPACITY)
>> +		return 0;
>> +
>
> If this for retaining cache hotness, should we look at
> SD_SHARE_PKG_RESOURCES instead of SD_SHARE_CPUCAPACITY?
>

Josh's patch only targets migrating tasks between threads of the same
core - as he points out, cache hotness shouldn't matter here.

Using SD_SHARE_PKG_RESOURCES here would mean freely migrating tasks between
any CPU of an LLC domain, which is quite likely something you do *not* want
to do.

>>      /*
>>       * Buddy candidates are cache hot:
>>       */
>> --
>> 2.28.0.163.g6104cc2f0b6-goog
>>

^ permalink raw reply	[flat|nested] 7+ messages in thread
* [tip: sched/core] sched/fair: Ignore cache hotness for SMT migration
  2020-08-04 19:34   ` [PATCH v2] " Josh Don
  2020-08-10  6:14     ` Srikar Dronamraju
@ 2020-08-27  7:54     ` tip-bot2 for Josh Don
  1 sibling, 0 replies; 7+ messages in thread
From: tip-bot2 for Josh Don @ 2020-08-27  7:54 UTC (permalink / raw)
  To: linux-tip-commits; +Cc: Josh Don, Peter Zijlstra (Intel), x86, LKML

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     ec73240b1627cddfd7cef018c7fa1c32e64a721e
Gitweb:        https://git.kernel.org/tip/ec73240b1627cddfd7cef018c7fa1c32e64a721e
Author:        Josh Don <joshdon@google.com>
AuthorDate:    Tue, 04 Aug 2020 12:34:13 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 26 Aug 2020 12:41:57 +02:00

sched/fair: Ignore cache hotness for SMT migration

SMT siblings share caches, so cache hotness should be irrelevant for
cross-sibling migration.

Signed-off-by: Josh Don <joshdon@google.com>
Proposed-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200804193413.510651-1-joshdon@google.com
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1a68a05..abdb54e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7402,6 +7402,10 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
 	if (unlikely(task_has_idle_policy(p)))
 		return 0;
 
+	/* SMT siblings share cache */
+	if (env->sd->flags & SD_SHARE_CPUCAPACITY)
+		return 0;
+
 	/*
 	 * Buddy candidates are cache hot:
 	 */

^ permalink raw reply related	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2020-08-27  7:55 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-04  0:06 [PATCH] sched/fair: ignore cache hotness for SMT migration Josh Don
2020-08-04 10:56 ` peterz
2020-08-04 19:24   ` Josh Don
2020-08-04 19:34   ` [PATCH v2] " Josh Don
2020-08-10  6:14     ` Srikar Dronamraju
2020-08-10  8:55       ` Valentin Schneider
2020-08-27  7:54     ` [tip: sched/core] sched/fair: Ignore " tip-bot2 for Josh Don

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