From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935107AbcHJSan (ORCPT ); Wed, 10 Aug 2016 14:30:43 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:40561 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935058AbcHJSak (ORCPT ); Wed, 10 Aug 2016 14:30:40 -0400 Date: Wed, 10 Aug 2016 14:47:32 +0200 From: Peter Zijlstra To: Mike Galbraith Cc: LKML Subject: Re: [patch] sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression Message-ID: <20160810124732.GF7141@twins.programming.kicks-ass.net> References: <1470827669.15624.16.camel@gmail.com> <20160810123033.GM30192@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160810123033.GM30192@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 10, 2016 at 02:30:33PM +0200, Peter Zijlstra wrote: > On Wed, Aug 10, 2016 at 01:14:29PM +0200, Mike Galbraith wrote: > > Hi Peter, > > > > While running ltp, the fates decided it was time for me to encounter > > the roughly 1 out of every 10 call failure below. As much as I run > > ltp, I'm a bit surprised that I (or anyone else) haven't met this > > before, but then the fates are known to be a tad fickle. > > > > getrusage04 0 TINFO : Expected timers granularity is 4000 us > > getrusage04 0 TINFO : Using 1 as multiply factor for max [us]time increment (1000+4000us)! > > getrusage04 0 TINFO : utime: 0us; stime: 179us > > getrusage04 0 TINFO : utime: 3751us; stime: 0us > > getrusage04 1 TFAIL : getrusage04.c:133: stime increased > 5000us: > > > > When applying the full rtime to either stime or utime, do not overwrite > > the previously tallied value. > > > > Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime") > > Signed-off-by: Mike Galbraith > > Cc: stable@vger.kernel.org # 4.3+ > > --- > > kernel/sched/cputime.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > --- a/kernel/sched/cputime.c > > +++ b/kernel/sched/cputime.c > > @@ -608,11 +608,13 @@ static void cputime_adjust(struct task_c > > > > if (utime == 0) { > > stime = rtime; > > + utime = prev->utime; > > goto update; > > } > > > > if (stime == 0) { > > utime = rtime; > > + stime = prev->stime; > > goto update; > > } > > This cannot be right; it violates that utime+stime==rtime. Let me try > and figure out what actually happens. Any idea where your [us]time are coming from? Do you end up in the vtime_accounting_enabled() path or not?