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Date:   Mon, 1 Mar 2021 22:38:49 +0530
From:   Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Rik van Riel <riel@surriel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Michael Neuling <mikey@neuling.org>,
        Gautham R Shenoy <ego@linux.vnet.ibm.com>,
        Parth Shah <parth@linux.ibm.com>
Subject: Re: [PATCH] sched/fair: Prefer idle CPU to cache affinity
Message-ID: <20210301170849.GK2028034@linux.vnet.ibm.com>
Reply-To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
References: <20210226164029.122432-1-srikar@linux.vnet.ibm.com>
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* Peter Zijlstra <peterz@infradead.org> [2021-03-01 16:40:33]:

> 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.

Thanks Peter, will take care of this along with other changes including
calling within rcu_read_lock and checking for tsds and psds after
rcu_dereference.

-- 
Thanks and Regards
Srikar Dronamraju