linux-kernel - Re: [PATCH 4/7] sched: Account rr and fifo tasks separately

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Date:	Wed, 2 Dec 2015 15:16:56 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 4/7] sched: Account rr and fifo tasks separately

On Wed, Dec 02, 2015 at 01:53:39PM +0100, Peter Zijlstra wrote:
> On Fri, Nov 13, 2015 at 03:22:06PM +0100, Frederic Weisbecker wrote:
> > In order to evaluate tick dependency, we need to account SCHED_RR and
> > SCHED_FIFO tasks separately as those policies don't have the same
> > preemption requirements.
> > 
> > We still keep rt_nr_running as a cache to avoid additions between nr_rr
> > and nr_fifo all over the place.
> 
> In which case you only need one of nr_fifo/nr_rr. Less accounting is
> better.
> 
> Pick the one you need for the nohz_full condition, and leave the other.
> A quick look at sched_can_stop_tick() seems to suggest nr_rr is the
> interesting one. nr_rr < 2 should allow stopping the tick.

Sounds pretty good! I'm going to do that!

Thanks!
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