linux-kernel - Re: [GIT PULL] cputime patch for 2.6.30-rc6

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Message-ID: <alpine.LSU.2.00.0905251316510.3539@fbirervta.pbzchgretzou.qr>
Date:	Mon, 25 May 2009 13:24:51 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Michael Abbott <michael@...neidae.co.uk>
Subject: Re: [GIT PULL] cputime patch for 2.6.30-rc6


On Monday 2009-05-25 13:09, Peter Zijlstra wrote:
>
>I really prefer using things like percpu_counter/vmstat that have error
>bounds that scale with the number of cpus in the system.
>
>We simply have to start educating people that numbers on the global
>state of the machine are inaccurate (they were anyway, because by the
>time the userspace bits that read the /proc file get scheduled again the
>numbers will have changed again).
>
>There's a variant of Heisenberg's uncertainty principle applicable to
>(parallel) computers in that one either gets concurrency or accuracy on
>global state, you cannot have both.
>
Inaccuracies are fine, esp. for something like monotic increasing
idle uptime.
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