Messages in this thread | | | Date | Sat, 28 Feb 2009 08:34:02 +0900 (JST) | Subject | Re: [PATCH] change cpuacct usage percpu format v2 | From | "KAMEZAWA Hiroyuki" <> |
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Ken Chen さんは書きました: > On Thu, Feb 26, 2009 at 11:29 PM, KAMEZAWA Hiroyuki > <kamezawa.hiroyu@jp.fujitsu.com> wrote: >> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> >> >> cpuacct.usage_percpu shows per cpu usage information via cgroupfs. >> It shows all "present" cpus information and "whose information ?" >> is explained just by index of data implicitly. >> >> IIRC, there is physical cpu hotplug system and it can remove >> cpus and change map. Considering a software which records >> this information pediodically(like sar), its better to show id of cpu >> in explict way. > > The new format carries a lot of overhead. I would think user space > software can record /sys/devices/system/cpu/present and use that to > map cpu index. > "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 ;)
A program which handles this kind of information tend to ignore hotplug event and continue to use informaton which it gathers at start-up and will not see updated information....as libnuma etc.
Thanks, -Kame
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