linux-kernel - Re: [PATCH v7 01/22] sched: Favour predetermined active CPU as migration destination

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Date:   Wed, 26 May 2021 13:36:27 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Quentin Perret <qperret@...gle.com>, Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        kernel-team@...roid.com
Subject: Re: [PATCH v7 01/22] sched: Favour predetermined active CPU as migration destination

On 26/05/21 14:32, Peter Zijlstra wrote:
> On Wed, May 26, 2021 at 12:14:20PM +0100, Valentin Schneider wrote:
>> ---
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 5226cc26a095..cd447c9db61d 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>
>> @@ -1954,19 +1953,15 @@ static int migration_cpu_stop(void *data)
>>  		if (pending) {
>>  			p->migration_pending = NULL;
>>  			complete = true;
>>  
>>  			if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask))
>>  				goto out;
>>  		}
>>  
>>  		if (task_on_rq_queued(p))
>> +			rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
>
>> @@ -2249,7 +2244,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
>>  			init_completion(&my_pending.done);
>>  			my_pending.arg = (struct migration_arg) {
>>  				.task = p,
>> +				.dest_cpu = dest_cpu,
>>  				.pending = &my_pending,
>>  			};
>>  
>> @@ -2257,6 +2252,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag
>>  		} else {
>>  			pending = p->migration_pending;
>>  			refcount_inc(&pending->refs);
>> +			pending->arg.dest_cpu = dest_cpu;
>>  		}
>>  	}
>
> Argh.. that might just work. But I'm thinking we wants comments this
> time around :-) This is even more subtle.

Lemme stare at it some more and sharpen my quill then.