linux-kernel - RE: [PATCH 1/3] sched: Add new API wake_up_if

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Date:	Wed, 3 Sep 2014 09:58:56 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>
CC:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	"Chakravarty, Souvik K" <souvik.k.chakravarty@...el.com>,
	"Liu, Changcheng" <changcheng.liu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
 idle cpu



> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Wednesday, September 03, 2014 5:54 PM
> To: Andy Lutomirski
> Cc: Liu, Chuansheng; linux-pm@...r.kernel.org; Rafael J. Wysocki; Daniel
> Lezcano; Wang, Xiaoming; Ingo Molnar; Chakravarty, Souvik K; Liu, Changcheng;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
> idle cpu
> 
> On Thu, Aug 21, 2014 at 02:21:51PM -0700, Andy Lutomirski wrote:
> > On Aug 18, 2014 3:52 AM, "Chuansheng Liu" <chuansheng.liu@...el.com>
> wrote:
> 
> > > +void wake_up_if_idle(int cpu)
> > > +{
> > > +       struct rq *rq = cpu_rq(cpu);
> > > +       unsigned long flags;
> > > +
> > > +       if (set_nr_if_polling(rq->idle)) {
> > > +               trace_sched_wake_idle_without_ipi(cpu);
> > > +       } else {
> > > +
> >
> > FWIW, adding:
> >
> > if (rq->curr != rq->idle)
> >     return;
> >
> > Right here could improve performance on large, mostly non-idle
> > systems.  It would skip the spinlock in most cases.
> >
> 
>  !is_idle_task() :-)
Thanks Peter and Andy, will refine the patches again:)


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