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

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Date:	Fri, 5 Sep 2008 18:15:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	balbir@...ux.vnet.ibm.com, Spencer Candland <spencer@...ehost.com>,
	dmitry.adamushko@...il.com, linux-kernel@...r.kernel.org
Subject: Re: Still seeing decreasing stime/utime


* Peter Zijlstra <a.p.zijlstra@...llo.nl> 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>

applied to tip/sched/urgent, thanks!

	Ingo
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