From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756141AbbJ1QLv (ORCPT ); Wed, 28 Oct 2015 12:11:51 -0400 Received: from mail-wi0-f177.google.com ([209.85.212.177]:35137 "EHLO mail-wi0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756054AbbJ1QLt (ORCPT ); Wed, 28 Oct 2015 12:11:49 -0400 Date: Wed, 28 Oct 2015 17:11:47 +0100 From: Frederic Weisbecker To: Hiroshi Shimamoto Cc: Peter Zijlstra , Ingo Molnar , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] cputime: fix invalid gtime Message-ID: <20151028161145.GA25958@lerouge> References: <7F861DC0615E0C47A872E6F3C5FCDDBD05F543FE@BPXM14GP.gisp.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7F861DC0615E0C47A872E6F3C5FCDDBD05F543FE@BPXM14GP.gisp.nec.co.jp> 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 On Wed, Oct 28, 2015 at 07:01:18AM +0000, Hiroshi Shimamoto wrote: > From: Hiroshi Shimamoto > > /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 now - tsk->vtime_snap, but tsk->vtime_snap > is only updated when vtime accounting is enabled. > > This patch makes task_gtime() just return gtime when vtime accounting > is not enabled. > > 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 > --- > kernel/sched/cputime.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > index 8cbc3db..f614ee9 100644 > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -786,6 +786,9 @@ cputime_t task_gtime(struct task_struct *t) > unsigned int seq; > cputime_t gtime; > > + if (!vtime_accounting_enabled()) > + return t->gtime; > + Obviously I completely messed up there. And task_cputime() has a similar issue but it happens to work due to vtime_snap_whence set to VTIME_SLEEPING when vtime doesn't run. Still it works at the cost of a seqcount read operation. Do you think you could fix it too (along with task_cputime_scaled())? I think those patches will also need a stable tag. Thanks! > do { > seq = read_seqbegin(&t->vtime_seqlock); > > -- > 1.8.3.1 >