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Message-ID: <7F861DC0615E0C47A872E6F3C5FCDDBD05F575AA@BPXM14GP.gisp.nec.co.jp> Date: Fri, 30 Oct 2015 00:46:39 +0000 From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com> To: Frederic Weisbecker <fweisbec@...il.com> CC: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: [PATCH v3 1/2] cputime: fix invalid gtime in proc From: Hiroshi Shimamoto <h-shimamoto@...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. Use context_tracking_is_enabled() to check if the vtime accounting on current cpu. In future we should check the state of cpu which is running target thread. 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@...jp.nec.com> Cc: stable@...r.kernel.org --- v2: Update ChangeLog to put the script and show the point. v3: Use context_tracking_is_enabled() instead of vtime_accounting_enabled(). kernel/sched/cputime.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 8cbc3db..63904e7 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 (!context_tracking_is_enabled()) + return t->gtime; + 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 majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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