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

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Date:	Thu, 21 Aug 2014 02:12:49 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"luto@...capital.net" <luto@...capital.net>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"mingo@...hat.com" <mingo@...hat.com>
CC:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Liu, Changcheng" <changcheng.liu@...el.com>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>,
	"Chakravarty, Souvik K" <souvik.k.chakravarty@...el.com>
Subject: RE: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
 idle cpu

Hello Daniel,

> -----Original Message-----
> From: Daniel Lezcano [mailto:daniel.lezcano@...aro.org]
> Sent: Thursday, August 21, 2014 9:54 AM
> To: Liu, Chuansheng; luto@...capital.net; peterz@...radead.org;
> rjw@...ysocki.net; mingo@...hat.com
> Cc: linux-pm@...r.kernel.org; linux-kernel@...r.kernel.org; Liu, Changcheng;
> Wang, Xiaoming; Chakravarty, Souvik K
> Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
> idle cpu
> 
> On 08/18/2014 10:37 AM, Chuansheng Liu wrote:
> > Implementing one new API wake_up_if_idle(), which is used to
> > wake up the idle CPU.
> 
> Is this patchset tested ? Did you check it solves the issue you were
> facing ?
We have done the basic test, and found the cores can exit C0 quickly with this patchset.
Basically once the _TIF_NEED_RESCHED is set, then the poll_idle() can be broken.

Please correct me if something is wrong, thanks.

> 
> > Suggested-by: Andy Lutomirski <luto@...capital.net>
> > Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.com>
> > ---
> >   include/linux/sched.h |    1 +
> >   kernel/sched/core.c   |   16 ++++++++++++++++
> >   2 files changed, 17 insertions(+)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 857ba40..3f89ac1 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
> >   extern struct sched_domain_topology_level *sched_domain_topology;
> >
> >   extern void set_sched_topology(struct sched_domain_topology_level *tl);
> > +extern void wake_up_if_idle(int cpu);
> >
> >   #ifdef CONFIG_SCHED_DEBUG
> >   # define SD_INIT_NAME(type)		.name = #type
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 1211575..adf104f 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct
> task_struct *p, int cpu)
> >   	}
> >   }
> >
> > +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 {
> > +		raw_spin_lock_irqsave(&rq->lock, flags);
> > +		if (rq->curr == rq->idle)
> > +			smp_send_reschedule(cpu);
> > +		/* Else cpu is not in idle, do nothing here */
> > +		raw_spin_unlock_irqrestore(&rq->lock, flags);
> > +	}
> > +}
> > +
> >   bool cpus_share_cache(int this_cpu, int that_cpu)
> >   {
> >   	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
> >
> 
> 
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