Date: Thu, 31 Mar 2016 12:47:05 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Steve Muckle <steve.muckle@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ingo Molnar <mingo@redhat.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Juri Lelli <Juri.Lelli@arm.com>,
        Patrick Bellasi <patrick.bellasi@arm.com>,
        Michael Turquette <mturquette@baylibre.com>
Subject: Re: [PATCH 1/2] sched/fair: move cpufreq hook to
 update_cfs_rq_load_avg()
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On Thu, Mar 31, 2016 at 11:50:40AM +0200, Vincent Guittot wrote:
> > In what case? Assuming you talk about a remove wakeup, no. Only if that
> > wakeup results in a preemption, which isn't a given.
> 
> yes, i was speaking about a remote wakeup.
> In the ttwu_queue_remote,  there is a call to smp_send_reschedule. Is
> there another way to add a remote task in the wake list ?

Right, but at that point we don't yet know how much util will change.

And doing that IPI unconditionally is expensive; see:

  518cd6234178 ("sched: Only queue remote wakeups when crossing cache boundaries")

13% regression on TCP_RR.