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From: Mel Gorman <mgorman@techsingularity.net>
To: Hillf Danton <hdanton@sina.com>
Cc: Juri Lelli <juri.lelli@redhat.com>,
	Barry Song <song.bao.hua@hisilicon.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 3/4] sched/fair: Do not replace recent_used_cpu with the new target
Date: Fri, 11 Dec 2020 09:45:40 +0000	[thread overview]
Message-ID: <20201211094540.GV3371@techsingularity.net> (raw)
In-Reply-To: <20201211093443.3259-1-hdanton@sina.com>

On Fri, Dec 11, 2020 at 05:34:43PM +0800, Hillf Danton wrote:
> On Fri, 11 Dec 2020 09:02:28 +0000 Mel Gorman wrote:
> >On Fri, Dec 11, 2020 at 02:25:42PM +0800, Hillf Danton wrote:
> >> On Tue,  8 Dec 2020 15:35:00 +0000 Mel Gorman wrote:
> >> > @@ -6277,17 +6277,13 @@ 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) &&
> >> >  	    (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
> >> >  	    cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) &&
> >> 
> >> Typo? Fix it in spin if so.
> >> 
> >
> >What typo?
> 
> After your change it is prev that we check against p->cpus_ptr instead of
> the recent CPU. Wonder the point to do such a check for returning the
> recent one.

Ah... yes, this is indeed wrong. It wouldn't affect Vincent's case
that showed a problem with a hackbench configuration (which I'm still
disappointed about as it's a trade-off depending on machine and workload)
but it allows a task to run on the wrong cpu if sched_setscheduler()
was called between wakeup events.

-- 
Mel Gorman
SUSE Labs

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WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@techsingularity.net>
To: Hillf Danton <hdanton@sina.com>
Cc: Peter Ziljstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Barry Song <song.bao.hua@hisilicon.com>,
	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 3/4] sched/fair: Do not replace recent_used_cpu with the new target
Date: Fri, 11 Dec 2020 09:45:40 +0000	[thread overview]
Message-ID: <20201211094540.GV3371@techsingularity.net> (raw)
In-Reply-To: <20201211093443.3259-1-hdanton@sina.com>

On Fri, Dec 11, 2020 at 05:34:43PM +0800, Hillf Danton wrote:
> On Fri, 11 Dec 2020 09:02:28 +0000 Mel Gorman wrote:
> >On Fri, Dec 11, 2020 at 02:25:42PM +0800, Hillf Danton wrote:
> >> On Tue,  8 Dec 2020 15:35:00 +0000 Mel Gorman wrote:
> >> > @@ -6277,17 +6277,13 @@ 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) &&
> >> >  	    (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) &&
> >> >  	    cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) &&
> >> 
> >> Typo? Fix it in spin if so.
> >> 
> >
> >What typo?
> 
> After your change it is prev that we check against p->cpus_ptr instead of
> the recent CPU. Wonder the point to do such a check for returning the
> recent one.

Ah... yes, this is indeed wrong. It wouldn't affect Vincent's case
that showed a problem with a hackbench configuration (which I'm still
disappointed about as it's a trade-off depending on machine and workload)
but it allows a task to run on the wrong cpu if sched_setscheduler()
was called between wakeup events.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2020-12-11  9:47 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08 15:34 [PATCH 0/4] Reduce scanning of runqueues in select_idle_sibling Mel Gorman
2020-12-08 15:34 ` Mel Gorman
2020-12-08 15:34 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-08 15:34   ` Mel Gorman
2020-12-08 16:13   ` Vincent Guittot
2020-12-08 16:13     ` Vincent Guittot
2020-12-08 15:34 ` [PATCH 2/4] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
2020-12-08 15:34   ` Mel Gorman
2020-12-08 16:03   ` Vincent Guittot
2020-12-08 16:03     ` Vincent Guittot
2020-12-08 16:30     ` Mel Gorman
2020-12-08 16:30       ` Mel Gorman
2020-12-09  5:28     ` Li, Aubrey
2020-12-09  5:28       ` Li, Aubrey
2020-12-09  9:05       ` Mel Gorman
2020-12-09  9:05         ` Mel Gorman
2020-12-09 11:07         ` Li, Aubrey
2020-12-09 11:07           ` Li, Aubrey
2020-12-09 11:33           ` Mel Gorman
2020-12-09 11:33             ` Mel Gorman
2020-12-10  5:18   ` Li, Aubrey
2020-12-10  5:18     ` Li, Aubrey
2020-12-10  9:32     ` Mel Gorman
2020-12-10  9:32       ` Mel Gorman
2020-12-08 15:35 ` [PATCH 3/4] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman
2020-12-08 15:35   ` Mel Gorman
2020-12-08 16:14   ` Vincent Guittot
2020-12-08 16:14     ` Vincent Guittot
2020-12-10  9:40     ` Vincent Guittot
2020-12-10  9:40       ` Vincent Guittot
2020-12-11  6:25   ` Hillf Danton
2020-12-11  9:02     ` Mel Gorman
2020-12-11  9:02       ` Mel Gorman
2020-12-11  9:34       ` Hillf Danton
2020-12-11  9:45         ` Mel Gorman [this message]
2020-12-11  9:45           ` Mel Gorman
2020-12-08 15:35 ` [PATCH 4/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman
2020-12-08 15:35   ` Mel Gorman
2020-12-08 16:15   ` Vincent Guittot
2020-12-08 16:15     ` Vincent Guittot
2020-12-09 14:37 ` [PATCH 0/4] Reduce scanning of runqueues in select_idle_sibling Mel Gorman
2020-12-09 14:37   ` Mel Gorman
2020-12-10  8:00   ` Vincent Guittot
2020-12-10  8:00     ` Vincent Guittot
2020-12-10  9:38     ` Vincent Guittot
2020-12-10  9:38       ` Vincent Guittot
2020-12-10 11:04       ` Mel Gorman
2020-12-10 11:04         ` Mel Gorman
2020-12-11  9:51         ` Vincent Guittot
2020-12-11  9:51           ` Vincent Guittot
2020-12-11 10:23           ` Mel Gorman
2020-12-11 10:23             ` Mel Gorman
2020-12-12 10:02             ` Vincent Guittot
2020-12-12 10:02               ` Vincent Guittot

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