linux-kernel - Re: [patch] sched: accurate user accounting

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Message-ID: <Pine.LNX.4.64.0703251854430.8043@linmac.oyster.ru>
Date:	Sun, 25 Mar 2007 18:57:18 +0400 (MSD)
From:	malc <av1474@...tv.ru>
To:	Con Kolivas <kernel@...ivas.org>
cc:	Ingo Molnar <mingo@...e.hu>,
	linux list <linux-kernel@...r.kernel.org>, zwane@...radead.org,
	ck list <ck@....kolivas.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch] sched: accurate user accounting

On Mon, 26 Mar 2007, Con Kolivas wrote:

> On Sunday 25 March 2007 23:06, malc wrote:
>> On Sun, 25 Mar 2007, Con Kolivas wrote:
>>> On Sunday 25 March 2007 21:46, Con Kolivas wrote:
>>>> On Sunday 25 March 2007 21:34, malc wrote:
>>>>> On Sun, 25 Mar 2007, Ingo Molnar wrote:
>>>>>> * Con Kolivas <kernel@...ivas.org> wrote:
>>>>>>> For an rsdl 0.33 patched kernel. Comments? Overhead worth it?
>>
>> [..snip..]
>>
>>> ---
>>> 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. This increases overhead slightly but
>>> avoids the problem of tick aliasing errors making accounting unreliable.
>>>
>>> Signed-off-by: Con Kolivas <kernel@...ivas.org>
>>> Signed-off-by: Ingo Molnar <mingo@...e.hu>
>>
>> [..snip..]
>>
>> Forgot to mention. Given that this goes into the kernel, shouldn't
>> Documentation/cpu-load.txt be amended/removed?
>
> Yes that's a good idea. Also there should be a sanity check because sometimes
> for some reason noone's been able to explain to me sched_clock gives a value
> which doesn't make sense (time appears to have gone backwards) and that will
> completely ruin the accounting from then on.

After running this new kernel for a while i guess i have hit this issue:
http://www.boblycat.org/~malc/apc/bad-load.png

Top and icewm's monitor do show incredibly huge load while in reality 
nothing like that is really happening. Both ad-hoc and `/proc/stat' (idle)
show normal CPU utilization (7% since i'm doing some A/V stuff in the
background)

-- 
vale
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