linux-kernel - Re: [PATCH] sched/fair: Prefer idle CPU to cache affinity

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Date:   Tue, 2 Mar 2021 15:34:25 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Parth Shah <parth@...ux.ibm.com>
Subject: Re: [PATCH] sched/fair: Prefer idle CPU to cache affinity

* Dietmar Eggemann <dietmar.eggemann@....com> [2021-03-02 10:53:06]:

> On 26/02/2021 17:40, Srikar Dronamraju wrote:
> 
> [...]
> 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 8a8bd7b13634..d49bfcdc4a19 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -5869,6 +5869,36 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
> >  	return this_eff_load < prev_eff_load ? this_cpu : nr_cpumask_bits;
> >  }
> > 
> > +static int prefer_idler_llc(int this_cpu, int prev_cpu, int sync)
> > +{
> > +	struct sched_domain_shared *tsds, *psds;
> > +	int pnr_busy, pllc_size, tnr_busy, tllc_size, diff;
> > +
> > +	tsds = rcu_dereference(per_cpu(sd_llc_shared, this_cpu));
> > +	tnr_busy = atomic_read(&tsds->nr_busy_cpus);
> > +	tllc_size = per_cpu(sd_llc_size, this_cpu);
> > +
> > +	psds = rcu_dereference(per_cpu(sd_llc_shared, prev_cpu));
> > +	pnr_busy = atomic_read(&psds->nr_busy_cpus);
> > +	pllc_size = per_cpu(sd_llc_size, prev_cpu);
> > +
> > +	/* No need to compare, if both LLCs are fully loaded */
> > +	if (pnr_busy == pllc_size && tnr_busy == pllc_size)
> 
>                                                      ^
>                                            shouldn't this be tllc_size ?

Yes, thanks for pointing out.

-- 
Thanks and Regards
Srikar Dronamraju