Messages in this thread | | | Subject | Re: [patch] sched: schedstat needs a diet | Date | Wed, 31 Oct 2007 02:06:01 -0700 | From | Rick Lindsley <> |
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On 10/18/07, Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote: > Good question indeed. How large is this memory footprint exactly ? If it > is as small as you say, I suspect that the real issue could be that > these variable are accessed by the scheduler critical paths and > therefore trash the caches. Maybe my wording was ambiguous, I meant to reduce cache line pollution when accessing these schedstat fields.
As the original author, it was always my intention that schedstats be low enough impact that it could be turned on all the time, if need be. That's why, for the most part, it does increments and decrements of counters and leaves the actual math to apps that might gather the data. Initial measurements showed that it was having no measurable impact on performance.
Of course, that was years ago too. Systems (and hardware) have changed considerably in that time. Are we talking theoretical cache pollution or measured? And if measured, what effect is it having?
(sorry for the late followup; was on vacation ...)
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