linux-kernel - Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

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Date:	Mon, 19 Aug 2013 12:58:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Fernando Luis Vazquez Cao <fernando_b1@....ntt.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

On Fri, Aug 16, 2013 at 07:12:09PM +0200, Frederic Weisbecker wrote:
> Or may be Peter could tell us as well. Peter, do you have a preference?

Still trying to wrap my head around it, but conceptually
get_cpu_iowait_time_us() doesn't make any kind of sense. iowait isn't
per cpu since effectively tasks that aren't running aren't assigned a
cpu (as Oleg already pointed out).

The fact that cpufreq 'needs' this just means that cpufreq is broken --
but I think I've said as much previously; cpufreq needs to stop living
in the partitioned-mp era and get dragged (kicking and screaming) into
the smp era.

I'm also not entirely clear on the 'desired' semantics here. Do we count
iowait time as idle or not?
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