linux-kernel - Re: process time

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Message-ID: <alpine.LFD.2.02.1109011226160.2723@ionos>
Date:	Thu, 1 Sep 2011 12:39:05 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org
Subject: Re: process time < thread time?

On Thu, 1 Sep 2011, Peter Zijlstra wrote:

> On Thu, 2011-09-01 at 11:56 +0200, Thomas Gleixner wrote:
> > The untested patch below should cure this.
> > 
> 
> > diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
> > index 58f405b..42378cb 100644
> > --- a/kernel/posix-cpu-timers.c
> > +++ b/kernel/posix-cpu-timers.c
> > @@ -250,7 +250,7 @@ void thread_group_cputime(struct task_struct *tsk,
> > struct task_cputime *times)
> >         do {
> >                 times->utime = cputime_add(times->utime, t->utime);
> >                 times->stime = cputime_add(times->stime, t->stime);
> > -               times->sum_exec_runtime += t->se.sum_exec_runtime;
> > +               times->sum_exec_runtime += task_sched_runtime(t);
> >         } while_each_thread(tsk, t);
> >  out:
> >         rcu_read_unlock(); 
> 
> I think we just deadlocked:

That's why I said untested :)
 
> cpu_clock_sample_group()
>   CPUCLOCK_SCHED: thread_group_sched_runtime()
>     task_rq_lock()        <-.
>     thread_group_cputime()  |
>       task_sched_runtime()  |
>        task_rq_lock() ------'
> 
> 
> Also, having to take locks here is sad, but yeah if we want to cure this
> there's not much we can do about that.

Yeah :(
 
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