Messages in this thread | | | Date | Fri, 27 Feb 2009 16:00:06 -0800 | Subject | Re: [PATCH] change cpuacct usage percpu format v2 | From | Ken Chen <> |
| |
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
| |