linux-kernel - Re: [PATCH 3/4] sched/fair: Do not replace recent_used

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Date:   Fri, 11 Dec 2020 09:02:28 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Peter Ziljstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Linux-ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/4] sched/fair: Do not replace recent_used_cpu with the
 new target

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?

> >  	    asym_fits_capacity(task_util, recent_used_cpu)) {
> > -		/*
> > -		 * Replace recent_used_cpu with prev as it is a potential
> > -		 * candidate for the next wake:
> > -		 */
> > -		p->recent_used_cpu = prev;
> >  		return recent_used_cpu;
> 
> I prefer to update the recent CPU after llc check.
> 

That would prevent recent_used_cpu leaving the LLC the task first
started on.

-- 
Mel Gorman
SUSE Labs