linux-kernel - Re: [patch 1/2] nohz: only wakeup a single target cpu when kicking a task

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Message-ID: <20201022125355.GA16049@lothringen>
Date:   Thu, 22 Oct 2020 14:53:55 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [patch 1/2] nohz: only wakeup a single target cpu when kicking a
 task

On Tue, Oct 20, 2020 at 03:52:45PM -0300, Marcelo Tosatti wrote:
> On Thu, Oct 15, 2020 at 01:40:53AM +0200, Frederic Weisbecker wrote:
> > Alternatively, we could rely on p->on_rq which is set to TASK_ON_RQ_QUEUED
> > at wake up time, prior to the schedule() full barrier. Of course that doesn't
> > mean that the task is actually the one running on the CPU but it's a good sign,
> > considering that we are running in nohz_full mode and it's usually optimized
> > for single task mode.
> 
> Unfortunately that would require exporting p->on_rq which is internal to
> the scheduler, locklessly.
> 
> (can surely do that if you prefer!)

May be:

    bool task_on_rq(struct task_struct *p) ?

Thanks.