Messages in this thread | | | Date | Sat, 28 Feb 2009 09:42:17 +0900 (JST) | Subject | Re: [PATCH] change cpuacct usage percpu format v2 | From | "KAMEZAWA Hiroyuki" <> |
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KAMEZAWA Hiroyuki wrote: > Ken Chen wrote: >> 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? >> > Are you saying the software should have hotplug script and send SIGHUP or > some to reload the present map ? > >> 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. >> > Sounds strange. I can't catch hat you want to say. > Ignore above, I caught, at last. I'll add text to documenation.
BTW, current interface to reset cpuacct (write ops) just reset specified level of cpuacct and will not clear other hierarchical levels. Doesn't this behavior confuse software ?
Thanks, -Kame
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