> Subject: Re: [PATCH v2] cputime: fix invalid gtime > > On Wed, Oct 28, 2015 at 07:01:18AM +0000, Hiroshi Shimamoto wrote: > > From: Hiroshi Shimamoto <h-shimam...@ct.jp.nec.com> > > > > /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 <h-shimam...@ct.jp.nec.com> > > --- > > 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.
Do you mean that task_cputime() and task_cputime_scaled() don't hit invalid behavior but have some extra operation cost which could be removed? Will look into it, and send patches with stable tag. thanks, Hiroshi > > Thanks! > > > > > do { > > seq = read_seqbegin(&t->vtime_seqlock); > > > > -- > > 1.8.3.1 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/