* Frederic Weisbecker <fweis...@gmail.com> wrote:
> 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 <h-shimam...@ct.jp.nec.com>
> > AuthorDate: Thu, 19 Nov 2015 16:47:28 +0100
> > Committer: Ingo Molnar <mi...@kernel.org>
> > 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 <h-shimam...@ct.jp.nec.com>
> > Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> > Cc: Chris Metcalf <cmetc...@ezchip.com>
> > Cc: Christoph Lameter <c...@linux.com>
> > Cc: Linus Torvalds <torva...@linux-foundation.org>
> > Cc: Luiz Capitulino <lcapitul...@redhat.com>
> > Cc: Mike Galbraith <efa...@gmx.de>
> > Cc: Paul E . McKenney <paul...@linux.vnet.ibm.com>
> > Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > Cc: Peter Zijlstra <pet...@infradead.org>
> > Cc: Rik van Riel <r...@redhat.com>
> > Cc: Thomas Gleixner <t...@linutronix.de>
> > Link:
> > http://lkml.kernel.org/r/1447948054-28668-2-git-send-email-fweis...@gmail.com
> > Signed-off-by: Ingo Molnar <mi...@kernel.org>
> > ---
>
> 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.
Absolutely, not sure why I forgot that tag - I added it for other recent fixes.
Greg, please consider applying this upstream fix to -stable as well:
2541117b0cf7 ("sched/cputime: Fix invalid gtime in proc")
Note, the commit will cherry-pick cleanly all the way back to v3.9 (released
2.5+
years ago), but it will only build on v3.14 and later kernels.
Thanks,
Ingo
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