Message-ID: <1490880922.4702.66.camel@gmx.de>
Subject: Re: [BUG nohz]: wrong user and system time accounting
From: Mike Galbraith <efault@gmx.de>
To: Rik van Riel <riel@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
        Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org
Date: Thu, 30 Mar 2017 15:35:22 +0200
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On Thu, 2017-03-30 at 09:02 -0400, Rik van Riel wrote:
> On Thu, 2017-03-30 at 14:51 +0200, Frederic Weisbecker wrote:

> > Also, why does it raise power consumption issues?
> 
> On a system without either nohz_full or nohz idle
> mode, skewed ticks result in CPU cores waking up
> at different times, and keeping an idle system
> consuming power for more time than it would if all
> the ticks happened simultaneously.

And if your server farm is mostly idle, that power savings may delay
your bankruptcy proceedings by a whole microsecond ;-)

Or more seriously, what skew does do on boxen of size X today is
something for perf to say.  At the time, removal was very bad for my 8
socket box, and allegedly caused huge SGI beasts in horrific pain.

	-Mike