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SubjectRe: [PATCH] change cpuacct usage percpu format v2
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On Fri, Feb 27, 2009 at 3:34 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> "a lot of" ? I talking about cpu hotplug and reading another file as
> /sys/devices/system/cpu/present every time before reading this file
> gives much much much more overhead ;)

yes, really a lot. CPU hotplug is an uncommon event. It happens
perhaps once a day? maybe once an hour?

User monitoring process usually reads usage_percpu at fairly high
rate, say once a sec. At each pass it will need to parse N number of
CPU index. The overhead is N_CPU * T, where T is time in second
between cpu hotplug event. Assume T = one day, on a moderate sized
64-CPU size machine, the overhead is:

64 * 86400 : 1, that's like 5.5 million to 1 ratio. To me that is
*high* overhead.

- Ken


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