From: Frederic Weisbecker <frederic@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
linux-kernel@vger.kernel.org,
Nitesh Narayan Lal <nitesh@redhat.com>,
Peter Xu <peterx@redhat.com>
Subject: Re: [patch 1/2] nohz: only wakeup a single target cpu when kicking a task
Date: Mon, 26 Oct 2020 15:42:53 +0100 [thread overview]
Message-ID: <20201026144253.GB120760@lothringen> (raw)
In-Reply-To: <20201015101235.GA2611@hirez.programming.kicks-ass.net>
On Thu, Oct 15, 2020 at 12:12:35PM +0200, Peter Zijlstra wrote:
> On Thu, Oct 15, 2020 at 01:40:53AM +0200, Frederic Weisbecker wrote:
> > > re tick_nohz_task_switch() being placed wrong, it should probably be
> > > placed before finish_lock_switch(). Something like so.
> > >
> > >
> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > index cf044580683c..5c92c959824f 100644
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -4084,6 +4084,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
> > > vtime_task_switch(prev);
> > > perf_event_task_sched_in(prev, current);
> > > finish_task(prev);
> > > + tick_nohz_task_switch();
> > > finish_lock_switch(rq);
> > > finish_arch_post_lock_switch();
> > > kcov_finish_switch(current);
> > > @@ -4121,7 +4122,6 @@ static struct rq *finish_task_switch(struct task_struct *prev)
> > > put_task_struct_rcu_user(prev);
> > > }
> > >
> > > - tick_nohz_task_switch();
> >
> > IIRC, we wanted to keep it outside rq lock because it shouldn't it...
>
> But now you've created a window with IRQs on and cause additional IRQ
> state changes.
>
> If you're really worried about rq->lock, I suppose we can do:
>
> rq_unlock(rq->lock);
> tick_nohz_task_switch();
> local_irq_enable();
>
> (much like we do at the beginning of __schedule for RCU)
Right. Well I'm not that worried about rq->lock though. If you're ok
with it I can just move it before finish_lock_switch().
Thanks.
next prev parent reply other threads:[~2020-10-26 14:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-07 18:01 [patch 0/2] nohz_full: only wakeup target CPUs when notifying new tick dependency (v2) Marcelo Tosatti
2020-10-07 18:01 ` [patch 1/2] nohz: only wakeup a single target cpu when kicking a task Marcelo Tosatti
2020-10-08 12:22 ` Peter Zijlstra
2020-10-08 17:54 ` Marcelo Tosatti
2020-10-08 19:54 ` Frederic Weisbecker
2020-10-13 17:13 ` Marcelo Tosatti
2020-10-14 8:33 ` Peter Zijlstra
2020-10-14 23:40 ` Frederic Weisbecker
2020-10-15 10:12 ` Peter Zijlstra
2020-10-26 14:42 ` Frederic Weisbecker [this message]
2020-10-20 18:52 ` Marcelo Tosatti
2020-10-22 12:53 ` Frederic Weisbecker
2020-10-08 14:59 ` Peter Xu
2020-10-08 15:28 ` Peter Zijlstra
2020-10-08 19:16 ` Peter Xu
2020-10-08 19:48 ` Frederic Weisbecker
2020-10-08 17:43 ` Marcelo Tosatti
2020-10-07 18:01 ` [patch 2/2] nohz: change signal tick dependency to wakeup CPUs of member tasks Marcelo Tosatti
2020-10-08 12:35 ` Peter Zijlstra
2020-10-08 18:04 ` Marcelo Tosatti
2020-10-08 19:11 [patch 0/2] nohz_full: only wakeup target CPUs when notifying new tick dependency (v3) Marcelo Tosatti
2020-10-08 19:11 ` [patch 1/2] nohz: only wakeup a single target cpu when kicking a task Marcelo Tosatti
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