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

From: Jan Engelhardt
Date: Mon May 25 2009 - 07:25:02 EST

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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