linux-kernel - Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6

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Date:   Thu, 14 May 2020 17:31:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Jirka Hladky <jhladky@...hat.com>, Phil Auld <pauld@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Hillf Danton <hdanton@...a.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Douglas Shakshober <dshaks@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Joe Mario <jmario@...hat.com>, Bill Gray <bgray@...hat.com>
Subject: Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load
 balancer v6

On Wed, May 13, 2020 at 04:30:23PM +0100, Mel Gorman wrote:
> Complete shot in the dark but restore adjust_numa_imbalance() and try
> this
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 1a9983da4408..0b31f4468d5b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2393,7 +2393,7 @@ static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
>  	struct rq_flags rf;
>  
>  #if defined(CONFIG_SMP)
> -	if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(), cpu)) {
> +	if (sched_feat(TTWU_QUEUE)) {

just saying that this has the risk of regressing other workloads, see:

  518cd6234178 ("sched: Only queue remote wakeups when crossing cache boundaries")

>  		sched_clock_cpu(cpu); /* Sync clocks across CPUs */
>  		ttwu_queue_remote(p, cpu, wake_flags);
>  		return;
> 
> -- 
> Mel Gorman
> SUSE Labs