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SubjectRe: Still seeing decreasing stime/utime
Peter Zijlstra wrote:
> On Sat, 2008-08-30 at 19:25 +0530, Balbir Singh wrote:
>> * Peter Zijlstra <> [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 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 <>
> Thanks Balbir!
> Acked-by: Peter Zijlstra <>

Ingo, could you please pick this one.


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