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sched/cputime: Fix getrusage(RUSAGE_THREAD) with nohz_full

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getrusage(RUSAGE_THREAD) with nohz_full may return shorter utime/stime
than the actual time.

task_cputime_adjusted() snapshots utime and stime and then adjust their
sum to match the scheduler maintained cputime.sum_exec_runtime.
Unfortunately in nohz_full, sum_exec_runtime is only updated once per
second in the worst case, causing a discrepancy against utime and stime
that can be updated anytime by the reader using vtime.

To fix this situation, perform an update of cputime.sum_exec_runtime
when the cputime snapshot reports the task as actually running while
the tick is disabled. The related overhead is then contained within the
relevant situations.

Reported-by: Hasegawa Hitomi <hasegawa-hitomi@fujitsu.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Hasegawa Hitomi <hasegawa-hitomi@fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Acked-by: Phil Auld <pauld@redhat.com>
Link: https://lore.kernel.org/r/20211026141055.57358-3-frederic@kernel.org
This commit is contained in:
Frederic Weisbecker 2021-10-26 16:10:55 +02:00 • committed by Thomas Gleixner
parent d58071a8a7
commit e7f2be115f
2 changed files with 12 additions and 5 deletions
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5
include/linux/sched/cputime.h
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@ -18,15 +18,16 @@
#endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
extern void task_cputime(struct task_struct *t,
extern bool task_cputime(struct task_struct *t,
u64 *utime, u64 *stime);
extern u64 task_gtime(struct task_struct *t);
#else
static inline void task_cputime(struct task_struct *t,
static inline bool task_cputime(struct task_struct *t,
u64 *utime, u64 *stime)
{
*utime = t->utime;
*stime = t->stime;
return false;
}
static inline u64 task_gtime(struct task_struct *t)