Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933426AbbLGQVq (ORCPT ); Mon, 7 Dec 2015 11:21:46 -0500 Received: from mail-wm0-f43.google.com ([74.125.82.43]:37383 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932076AbbLGQVo (ORCPT ); Mon, 7 Dec 2015 11:21:44 -0500 Date: Mon, 7 Dec 2015 17:21:36 +0100 From: Frederic Weisbecker To: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, efault@gmx.de, tglx@linutronix.de, peterz@infradead.org, cmetcalf@ezchip.com, paulmck@linux.vnet.ibm.com, h-shimamoto@ct.jp.nec.com, mingo@kernel.org, lcapitulino@redhat.com, hpa@zytor.com, riel@redhat.com, cl@linux.com Cc: linux-tip-commits@vger.kernel.org Subject: Re: [tip:locking/core] sched/cputime: Fix invalid gtime in proc Message-ID: <20151207162132.GA20032@lerouge> References: <1447948054-28668-2-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3465 Lines: 96 On Fri, Dec 04, 2015 at 03:53:13AM -0800, tip-bot for Hiroshi Shimamoto wrote: > Commit-ID: 2541117b0cf79977fa11a0d6e17d61010677bd7b > Gitweb: http://git.kernel.org/tip/2541117b0cf79977fa11a0d6e17d61010677bd7b > Author: Hiroshi Shimamoto > AuthorDate: Thu, 19 Nov 2015 16:47:28 +0100 > Committer: Ingo Molnar > CommitDate: Fri, 4 Dec 2015 10:18:49 +0100 > > sched/cputime: Fix invalid gtime in proc > > /proc/stats shows invalid gtime when the thread is running in guest. > When vtime accounting is not enabled, we cannot get a valid delta. > The delta is calculated with now - tsk->vtime_snap, but tsk->vtime_snap > is only updated when vtime accounting is runtime enabled. > > This patch makes task_gtime() just return gtime without computing the > buggy non-existing tickless delta when vtime accounting is not enabled. > > Use context_tracking_is_enabled() to check if vtime is accounting on > some cpu, in which case only we need to check the tickless delta. This > way we fix the gtime value regression on machines not running nohz full. > > The kernel config contains CONFIG_VIRT_CPU_ACCOUNTING_GEN=y and > CONFIG_NO_HZ_FULL_ALL=n and boot without nohz_full. > > I ran and stop a busy loop in VM and see the gtime in host. > Dump the 43rd field which shows the gtime in every second: > > # while :; do awk '{print $3" "$43}' /proc/3955/task/4014/stat; sleep 1; done > S 4348 > R 7064566 > R 7064766 > R 7064967 > R 7065168 > S 4759 > S 4759 > > During running busy loop, it returns large value. > > After applying this patch, we can see right gtime. > > # while :; do awk '{print $3" "$43}' /proc/10913/task/10956/stat; sleep 1; done > S 5338 > R 5365 > R 5465 > R 5566 > R 5666 > S 5726 > S 5726 > > Signed-off-by: Hiroshi Shimamoto > Signed-off-by: Frederic Weisbecker > Signed-off-by: Peter Zijlstra (Intel) > Cc: Chris Metcalf > Cc: Christoph Lameter > Cc: Linus Torvalds > Cc: Luiz Capitulino > Cc: Mike Galbraith > Cc: Paul E . McKenney > Cc: Paul E. McKenney > Cc: Peter Zijlstra > Cc: Rik van Riel > Cc: Thomas Gleixner > Link: http://lkml.kernel.org/r/1447948054-28668-2-git-send-email-fweisbec@gmail.com > Signed-off-by: Ingo Molnar > --- Thanks for applying the patchset! However we may want to backport this one, it's a regression fix affecting CONFIG_NO_HZ_FULL=y with nohz_full off (99% of many distros defaults). Thanks. > kernel/sched/cputime.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > index 26a5446..05de80b 100644 > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -788,6 +788,9 @@ cputime_t task_gtime(struct task_struct *t) > unsigned int seq; > cputime_t gtime; > > + if (!context_tracking_is_enabled()) > + return t->gtime; > + > do { > seq = read_seqbegin(&t->vtime_seqlock); > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/