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

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Date:   Mon, 1 Mar 2021 16:40:33 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Ingo Molnar <mingo@...nel.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>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        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

On Fri, Feb 26, 2021 at 10:10:29PM +0530, Srikar Dronamraju wrote:
> +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);
> +

nr_busy_cpus is NO_HZ_COMMON So this code that consumes it should be
too.