Messages in this thread | | | From | Al Boldi <> | Subject | Re: [patch] sched: accurate user accounting | Date | Mon, 26 Mar 2007 08:11:18 +0300 |
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Con Kolivas wrote: > > Ok this one is heavily tested. Please try it when you find the time.
It's better, but still skewed. Try two chew.c's; they account 80% each.
> --- > Currently we only do cpu accounting to userspace based on what is > actually happening precisely on each tick. The accuracy of that > accounting gets progressively worse the lower HZ is. As we already keep > accounting of nanosecond resolution we can accurately track user cpu, > nice cpu and idle cpu if we move the accounting to update_cpu_clock with > a nanosecond cpu_usage_stat entry.
That's great and much needed, but this is still probed; so what's wrong with doing it in-lined?
> This increases overhead slightly but > avoids the problem of tick aliasing errors making accounting unreliable.
Higher scheduling accuracy may actually offset any overhead incurred, so it's well worth it; and if it's in-lined it should mean even less overhead.
> + /* Sanity check. It should never go backwards or ruin accounting > */ + if (unlikely(now < p->last_ran)) > + goto out_set;
If sched_clock() goes backwards, why not fix it, instead of hacking around it?
Thanks!
-- Al
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