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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
View file

@ -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)

12
kernel/sched/cputime.c
View file

@ -615,7 +615,8 @@ void task_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *st)
.sum_exec_runtime = p->se.sum_exec_runtime,
};
task_cputime(p, &cputime.utime, &cputime.stime);
if (task_cputime(p, &cputime.utime, &cputime.stime))
cputime.sum_exec_runtime = task_sched_runtime(p);
cputime_adjust(&cputime, &p->prev_cputime, ut, st);
}
EXPORT_SYMBOL_GPL(task_cputime_adjusted);
@ -828,19 +829,21 @@ u64 task_gtime(struct task_struct *t)
* add up the pending nohz execution time since the last
* cputime snapshot.
*/
void task_cputime(struct task_struct *t, u64 *utime, u64 *stime)
bool task_cputime(struct task_struct *t, u64 *utime, u64 *stime)
{
struct vtime *vtime = &t->vtime;
unsigned int seq;
u64 delta;
int ret;
if (!vtime_accounting_enabled()) {
*utime = t->utime;
*stime = t->stime;
return;
return false;
}
do {
ret = false;
seq = read_seqcount_begin(&vtime->seqcount);
*utime = t->utime;
@ -850,6 +853,7 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime)
if (vtime->state < VTIME_SYS)
continue;
ret = true;
delta = vtime_delta(vtime);
/*
@ -861,6 +865,8 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime)
else
*utime += vtime->utime + delta;
} while (read_seqcount_retry(&vtime->seqcount, seq));
return ret;
}
static int vtime_state_fetch(struct vtime *vtime, int cpu)