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Message-ID: <20200417105754.GY20730@hirez.programming.kicks-ass.net>
Date: Fri, 17 Apr 2020 12:57:54 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: vpillai <vpillai@...italocean.com>,
Nishanth Aravamudan <naravamudan@...italocean.com>,
Julien Desfossez <jdesfossez@...italocean.com>,
mingo@...nel.org, tglx@...utronix.de, pjt@...gle.com,
torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
Aubrey Li <aubrey.intel@...il.com>, aubrey.li@...ux.intel.com,
Valentin Schneider <valentin.schneider@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Joel Fernandes <joelaf@...gle.com>, joel@...lfernandes.org,
Aaron Lu <aaron.lu@...ux.alibaba.com>
Subject: Re: [RFC PATCH 07/13] sched: Add core wide task selection and
scheduling.
On Thu, Apr 16, 2020 at 04:32:28PM -0700, Tim Chen wrote:
>
>
> On 4/14/20 6:35 AM, Peter Zijlstra wrote:
> > On Wed, Mar 04, 2020 at 04:59:57PM +0000, vpillai wrote:
> >> +static struct task_struct *
> >> +pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> >> +{
> >> + struct task_struct *next, *max = NULL;
> >> + const struct sched_class *class;
> >> + const struct cpumask *smt_mask;
> >> + int i, j, cpu;
> >> + bool need_sync = false;
> >
> > AFAICT that assignment is superfluous. Also, you violated the inverse
> > x-mas tree.
> >
> >> +
> >> + cpu = cpu_of(rq);
> >> + if (cpu_is_offline(cpu))
> >> + return idle_sched_class.pick_next_task(rq);
> >
> > Are we actually hitting this one?
> >
>
> I did hit this race when I was testing taking cpu offline and online,
> which prompted the check of cpu being offline.
This is the schedule from the stop task to the idle task I presume,
there should really not be any other. And at that point the rq had
better be empty, so why didn't the normal task selection work?
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