linux-kernel - Re: [PATCH v2] fix idle ticks in cpu summary line of /proc/stat

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Date:	Thu, 29 Mar 2012 12:42:22 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Michal Hocko <mhocko@...e.cz>
cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] fix idle ticks in cpu summary line of /proc/stat

On Tue, 13 Mar 2012, Michal Hocko wrote:

> OK, so the updated version of the patch looks like this. I am sorry but
> I had time to only compile test this...
> ---
> >From d12247f14c5f8b00ae97a87442f62e49227a759b Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.cz>
> Date: Mon, 12 Mar 2012 13:11:38 +0100
> Subject: [PATCH] nohz: fix idle ticks in cpu summary line of /proc/stat
> 
> Git commit 09a1d34f8535ecf9 "nohz: Make idle/iowait counter update
> conditional" introduced a bug in regard to cpu hotplug. The effect is
> that the number of idle ticks in the cpu summary line in /proc/stat is
> still counting ticks for offline cpus.
> 
> Reproduction is easy, just start a workload that keeps all cpus busy,
> switch off one or more cpus and then watch the idle field in top.
> On a dual-core with one cpu 100% busy and one offline cpu you will get
> something like this:
> 
> %Cpu(s): 48.7 us,  1.3 sy,  0.0 ni, 50.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
> 
> The problem is that an offline cpu still has ts->idle_active == 1.
> To fix this we should make sure that the cpu is online when calling
> get_cpu_idle_time_us and get_cpu_iowait_time_us.
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
> Reported-by: Martin Schwidefsky <schwidefsky@...ibm.com>

Martin, does that solve the problem for you ?

Thanks,

	tglx
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