linux-kernel - Re: [RFC 1/2] sched/fair: Fix load

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Message-ID: <20170512204754.GK4626@worktop.programming.kicks-ass.net>
Date:   Fri, 12 May 2017 22:47:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Austin Christ <austinwc@...eaurora.org>,
        Tyler Baicar <tbaicar@...eaurora.org>
Subject: Re: [RFC 1/2] sched/fair: Fix load_balance() affinity redo path

On Fri, May 12, 2017 at 11:01:37AM -0600, Jeffrey Hugo wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d711093..8f783ba 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8219,8 +8219,19 @@ static int load_balance(int this_cpu, struct rq *this_rq,
>  
>  		/* All tasks on this runqueue were pinned by CPU affinity */
>  		if (unlikely(env.flags & LBF_ALL_PINNED)) {
> +			struct cpumask tmp;

You cannot have cpumask's on stack.

> +
> +			/* Cpumask of all initially possible busiest cpus. */
> +			cpumask_copy(&tmp, sched_domain_span(env.sd));
> +			cpumask_clear_cpu(env.dst_cpu, &tmp);

You forgot to mask with cpu_active_mask.

> +
>  			cpumask_clear_cpu(cpu_of(busiest), cpus);
> -			if (!cpumask_empty(cpus)) {
> +			/*
> +			 * Go back to "redo" iff the load-balance cpumask
> +			 * contains other potential busiest cpus for the
> +			 * current sched domain.
> +			 */
> +			if (cpumask_intersects(cpus, &tmp)) {
>  				env.loop = 0;
>  				env.loop_break = sched_nr_migrate_break;
>  				goto redo;