linux-kernel - Re: [PATCH] process cputimer is moving faster than its corresponding clock

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Message-ID: <1365990909.29519.6.camel@Wailaba2>
Date:	Sun, 14 Apr 2013 21:55:09 -0400
From:	Olivier Langlois <olivier@...llion01.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, tglx@...utronix.de, fweisbec@...il.com,
	schwidefsky@...ibm.com, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] process cputimer is moving faster than its
 corresponding clock

On Fri, 2013-04-12 at 11:16 +0200, Peter Zijlstra wrote:
> On Wed, 2013-04-10 at 11:48 -0400, Olivier Langlois wrote:
> > Please explain how expensive it is. All I am seeing is a couple of
> > additions.
> 
> Let me start with this, since your earlier argument also refers to
> this.
> 
> So yes it does look simple and straight fwd, only one addition. However
> its an atomic operation across all threads of the same process. Imagine
> a single process with 512 threads, all running on a separate cpu.
> 
Peter,

It now makes perfect sense. Thank you for your explanation. It is
showing me an aspect that I did overlook.

Greetings,


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