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Date: Tue, 10 Nov 2009 20:23:27 +0100 From: Oleg Nesterov <oleg@...hat.com> To: Stanislaw Gruszka <sgruszka@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org>, Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>, Spencer Candland <spencer@...ehost.com>, linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu> Subject: Re: utime/stime decreasing on thread exit On 11/10, Stanislaw Gruszka wrote: > > On Tue, Nov 10, 2009 at 06:40:08PM +0100, Oleg Nesterov wrote: > > > > > > Or stay with task_cputime_expired() but only if cputimer is currently running. > > > > Oh. I forgot this code completely, can't comment. > > > > Can't we ensure that fastpath_timer_check() never do while_each_thread() ? > > Removing possibility to call while_each_tread() from fastpath_timer_check() > was exactly my intension here, perhaps I was not clear. Yes, yes, I understand. I meant, perhaps we can ensure this shouldn't happen "by design", instead of checking ->running in fastpath_timer_check(). > > IOW, if sig->cputime_expires != 0 then ->running must be true. > > At least, shouldn't stop_process_timers() clear sig->cputime_expires ? > > I'm going to think about that. However as far seems, checking ->running > explicitly and goto slow patch when is not true is safer solution. Yes, agreed. Still. check_process_timers() updates sig->cputime_expires at the end, but it never clears it. For example, if (sched_expires != 0 && (sig->cputime_expires.sched_exp == 0 || sig->cputime_expires.sched_exp > sched_expires)) sig->cputime_expires.sched_exp = sched_expires; Why? Now suppose that (say) sig->cputime_expires.sched_exp != 0, there are no cpu timers, ->running == F. In this case fastpath_timer_check() always returns T and triggers the slow path which does nothing, not good. But yes, I agree, probably we should start with the simple/safe change as you suggested. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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