linux-kernel - Re: Still seeing decreasing stime/utime

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Message-ID: <48BCECF9.5060104@linux.vnet.ibm.com>
Date:	Tue, 02 Sep 2008 13:06:25 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Spencer Candland <spencer@...ehost.com>,
	dmitry.adamushko@...il.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: Still seeing decreasing stime/utime

Peter Zijlstra wrote:
> On Sat, 2008-08-30 at 19:25 +0530, Balbir Singh wrote:
>> * Peter Zijlstra <a.p.zijlstra@...llo.nl> [2008-08-30 13:27:36]:
>>
>>> On Sat, 2008-08-30 at 11:26 +0530, Balbir Singh wrote:
>>>> Spencer Candland wrote:
>>>>>> Here is an experimental patch (I've just compiled and booted a machine
>>>>>> with it, I am unable to reproduce your problem), could you please test
>>>>>> it for me and see if it helps solve the problem
>>>>> Looks like this fixed it.  I have been testing this for the last 16
>>>>> hours and everything is looking good.
>>>>>
>>>> Excellent! Ingo, Peter, do you like the patch? If so, could you please pick it
>>>> up Ingo. I think we should even push the fix to stable releases.
>>> Looks good, except for the issue you yourself earlier raised, a few of
>>> those functions looks too large to be inlined.
>>>
>> Here's the updated revision with task_*time functions moved to sched.c
>> and inlining removed, except for task_gtime(). I've compiled and
>> booted a machine (x86_64) with this patch applied.
>>
>> Reported-by: spencer@...ehost.com
>>
>> Spencer reported a problem where utime and stime were going negative despite
>> the fixes in commit b27f03d4bdc145a09fb7b0c0e004b29f1ee555fa. The suspected
>> reason for the problem is that signal_struct maintains it's own utime and
>> stime (of exited tasks), these are not updated using the new task_utime()
>> routine, hence sig->utime can go backwards and cause the same problem
>> to occur (sig->utime, adds tsk->utime and not task_utime()). This patch
>> fixes the problem
>>
>> TODO: using max(task->prev_utime, derived utime) works for now, but a more
>> generic solution is to implement cputime_max() and use the cputime_gt()
>> function for comparison.
>>
>> Comments?
>>
>> Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
> 
> Thanks Balbir!
> 
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

Ingo, could you please pick this one.

-- 
	Thanks,
	Balbir
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