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From: Mel Gorman <mgorman@techsingularity.net>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Barry Song <song.bao.hua@hisilicon.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Peter Ziljstra <peterz@infradead.org>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Linux-ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/4] sched/fair: Do not replace recent_used_cpu with the new target
Date: Tue, 8 Dec 2020 11:02:44 +0000	[thread overview]
Message-ID: <20201208110244.GH3371@techsingularity.net> (raw)
In-Reply-To: <842ef1db-49d1-7d05-997b-1562383cdd28@arm.com>

On Tue, Dec 08, 2020 at 10:57:29AM +0100, Dietmar Eggemann wrote:
> On 07/12/2020 10:15, Mel Gorman wrote:
> > After select_idle_sibling, p->recent_used_cpu is set to the
> > new target. However on the next wakeup, prev will be the same as
> 
> I'm confused here. Isn't current->recent_used_cpu set to 'cpu =
> smp_processor_id()' after sis()? Looking at v5.10-rc6.

If you are referring to this;

               if (want_affine)
                       current->recent_used_cpu = cpu;

then it gets removed by the path. That replaces recent_used_cpu with the
wakers CPU which still works but the hit rate is lower.

> 
> [...]
> 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 23934dbac635..01b38fc17bca 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6274,6 +6274,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
> >  
> >  	/* Check a recently used CPU as a potential idle candidate: */
> >  	recent_used_cpu = p->recent_used_cpu;
> > +	p->recent_used_cpu = prev;
> >  	if (recent_used_cpu != prev &&
> >  	    recent_used_cpu != target &&
> >  	    cpus_share_cache(recent_used_cpu, target) &&
> 
> p->recent_used_cpu is already set to prev in this if condition.
> 

That can be removed as redundant, I'll fix it.

-- 
Mel Gorman
SUSE Labs

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WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@techsingularity.net>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Barry Song <song.bao.hua@hisilicon.com>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Ziljstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Linux-ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/4] sched/fair: Do not replace recent_used_cpu with the new target
Date: Tue, 8 Dec 2020 11:02:44 +0000	[thread overview]
Message-ID: <20201208110244.GH3371@techsingularity.net> (raw)
In-Reply-To: <842ef1db-49d1-7d05-997b-1562383cdd28@arm.com>

On Tue, Dec 08, 2020 at 10:57:29AM +0100, Dietmar Eggemann wrote:
> On 07/12/2020 10:15, Mel Gorman wrote:
> > After select_idle_sibling, p->recent_used_cpu is set to the
> > new target. However on the next wakeup, prev will be the same as
> 
> I'm confused here. Isn't current->recent_used_cpu set to 'cpu =
> smp_processor_id()' after sis()? Looking at v5.10-rc6.

If you are referring to this;

               if (want_affine)
                       current->recent_used_cpu = cpu;

then it gets removed by the path. That replaces recent_used_cpu with the
wakers CPU which still works but the hit rate is lower.

> 
> [...]
> 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 23934dbac635..01b38fc17bca 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6274,6 +6274,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
> >  
> >  	/* Check a recently used CPU as a potential idle candidate: */
> >  	recent_used_cpu = p->recent_used_cpu;
> > +	p->recent_used_cpu = prev;
> >  	if (recent_used_cpu != prev &&
> >  	    recent_used_cpu != target &&
> >  	    cpus_share_cache(recent_used_cpu, target) &&
> 
> p->recent_used_cpu is already set to prev in this if condition.
> 

That can be removed as redundant, I'll fix it.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2020-12-08 11:03 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-07  9:15 [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Mel Gorman
2020-12-07  9:15 ` Mel Gorman
2020-12-07  9:15 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-07  9:15   ` Mel Gorman
2020-12-07 15:05   ` Vincent Guittot
2020-12-07 15:05     ` Vincent Guittot
2020-12-08 10:07   ` Dietmar Eggemann
2020-12-08 10:07     ` Dietmar Eggemann
2020-12-08 10:59     ` Mel Gorman
2020-12-08 10:59       ` Mel Gorman
2020-12-08 13:24       ` Vincent Guittot
2020-12-08 13:24         ` Vincent Guittot
2020-12-08 13:36         ` Mel Gorman
2020-12-08 13:36           ` Mel Gorman
2020-12-08 13:43           ` Vincent Guittot
2020-12-08 13:43             ` Vincent Guittot
2020-12-08 13:53             ` Mel Gorman
2020-12-08 13:53               ` Mel Gorman
2020-12-08 14:47               ` Vincent Guittot
2020-12-08 14:47                 ` Vincent Guittot
2020-12-08 15:12                 ` Mel Gorman
2020-12-08 15:12                   ` Mel Gorman
2020-12-08 15:19                   ` Vincent Guittot
2020-12-08 15:19                     ` Vincent Guittot
2020-12-07  9:15 ` [PATCH 2/4] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman
2020-12-07  9:15   ` Mel Gorman
2020-12-08  9:57   ` Dietmar Eggemann
2020-12-08  9:57     ` Dietmar Eggemann
2020-12-08 11:02     ` Mel Gorman [this message]
2020-12-08 11:02       ` Mel Gorman
2020-12-07  9:15 ` [PATCH 3/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman
2020-12-07  9:15   ` Mel Gorman
2020-12-07 15:06   ` Vincent Guittot
2020-12-07 15:06     ` Vincent Guittot
2020-12-07  9:15 ` [PATCH 4/4] sched/fair: Avoid revisiting CPUs multiple times during select_idle_sibling Mel Gorman
2020-12-07  9:15   ` Mel Gorman
2020-12-07 15:04 ` [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Vincent Guittot
2020-12-07 15:04   ` Vincent Guittot
2020-12-07 15:42   ` Mel Gorman
2020-12-07 15:42     ` Mel Gorman
2020-12-08  2:06     ` Li, Aubrey
2020-12-08  2:06       ` Li, Aubrey

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