linux-kernel - Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable again and shut down on idle)

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Message-ID: <alpine.DEB.2.20.1601261222020.1964@east.gentwo.org>
Date:	Tue, 26 Jan 2016 12:22:42 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
cc:	Michal Hocko <mhocko@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable
 again and shut down on idle)

On Tue, 26 Jan 2016, Mike Galbraith wrote:

> On Tue, 2016-01-26 at 10:26 -0600, Christoph Lameter wrote:
> > On Tue, 26 Jan 2016, Mike Galbraith wrote:
> >
> > > > Why would the deferring cause this overhead?
> > >
> > > Because we schedule to idle cores aggressively, thus we may pop in and
> > > out of idle at high frequency.
> >
> > Whats the point of going idle if you have things to do soon?
>
> When a task schedules off, how do you know it'll be back at all, much
> less soon?

Ok so you are running an artificial benchmark that always gets the
system running again when it decides to go idle?