From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938959AbcHJS5e (ORCPT ); Wed, 10 Aug 2016 14:57:34 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:36256 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938782AbcHJS5b (ORCPT ); Wed, 10 Aug 2016 14:57:31 -0400 Message-ID: <1470855448.4840.2.camel@gmail.com> Subject: Re: [patch] sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression From: Mike Galbraith To: Peter Zijlstra Cc: LKML Date: Wed, 10 Aug 2016 20:57:28 +0200 In-Reply-To: <20160810123033.GM30192@twins.programming.kicks-ass.net> References: <1470827669.15624.16.camel@gmail.com> <20160810123033.GM30192@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="us-ascii" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2016-08-10 at 14:30 +0200, Peter Zijlstra wrote: > On Wed, Aug 10, 2016 at 01:14:29PM +0200, Mike Galbraith wrote: > > --- 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. How about this instead. sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression Roughly 10% of the time, ltp testcase getrusage04 fails: 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: If ->sum_exec_runtime has moved beyond the rtime of ->prev_cputime, but no time has as yet been accounted to the task, bail. Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime") Signed-off-by: Mike Galbraith Cc: stable@vger.kernel.org # 4.3+ --- kernel/sched/cputime.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -606,6 +606,13 @@ static void cputime_adjust(struct task_c stime = curr->stime; utime = curr->utime; + /* + * sum_exec_runtime has moved, but nothing has yet been + * accounted to the task, there's nothing to update. + */ + if (utime + stime == 0) + goto out; + if (utime == 0) { stime = rtime; goto update;