lkml.org 
[lkml]   [2007]   [Mar]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch] sched: accurate user accounting
Date
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

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-03-26 07:11    [W:0.024 / U:0.672 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site