linux-kernel - Re: [PATCH 2/8] vtime: Use consistent clocks among nohz accounting

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Date:	Mon, 03 Jun 2013 11:47:17 +0200
From:	Stefan Seyfried <stefan.seyfried@...glemail.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH 2/8] vtime: Use consistent clocks among nohz accounting

Am 20.05.2013 18:01, schrieb Frederic Weisbecker:
> While computing the cputime delta of dynticks CPUs,
> we are mixing up clocks of differents natures:

[...]

> As a consequence, some strange behaviour with unstable tsc
> has been observed such as non progressing constant zero cputime.
> (The 'top' command showing no load).

This happens for example on my trusty ThinkPad X200s (family 6 model 23
stepping 10 Core 2 duo), seriously confusing its user (me :-).

> Fix this by only using local_clock(), or its irq safe/remote
> equivalent, in vtime code.
> 
> Reported-by: Mike Galbraith <efault@....de>
> Suggested-by: Mike Galbraith <efault@....de>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
> Cc: Mike Galbraith <efault@....de>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

FWIW:
Tested-by: Stefan Seyfried <seife+dev@...systems.com>

This patch fixes the 0% CPU issue on openSUSE Factory kernels for me.

Best regards,

	Stefan
-- 
Stefan Seyfried
Linux Consultant & Developer -- GPG Key: 0x731B665B

B1 Systems GmbH
Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de
GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537
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