linux-kernel - Re: [PATCH 3/4 v2] nohz: Fix idle/iowait counts going backwards

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Message-ID: <20140507142321.GA2844@laptop.programming.kicks-ass.net>
Date:	Wed, 7 May 2014 16:23:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Fernando Luis Vazquez Cao <fernando_b1@....ntt.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 3/4 v2] nohz: Fix idle/iowait counts going backwards

On Wed, May 07, 2014 at 03:41:33PM +0200, Denys Vlasenko wrote:
> With this change, "iowait-ness" of every idle period is decided
> at the moment it starts:
> if this CPU's run-queue had tasks waiting on I/O, then this idle
> period's duration will be added to iowait_sleeptime.
> 
> This fixes the bug where iowait and/or idle counts could go backwards,
> but iowait accounting is not precise (it can show more iowait
> that there really is).
> 

NAK on this, the thing going backwards is a symptom of the bug, not an
actual bug itself.
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