* Frederic Weisbecker <fweisbec@xxxxxxxxx> 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-shimamoto@xxxxxxxxxxxxx> > > AuthorDate: Thu, 19 Nov 2015 16:47:28 +0100 > > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > > 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-shimamoto@xxxxxxxxxxxxx> > > Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > > Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx> > > Cc: Christoph Lameter <cl@xxxxxxxxx> > > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx> > > Cc: Mike Galbraith <efault@xxxxxx> > > Cc: Paul E . McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > Cc: Rik van Riel <riel@xxxxxxxxxx> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Link: http://lkml.kernel.org/r/1447948054-28668-2-git-send-email-fweisbec@xxxxxxxxx > > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> > > --- > > 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html