Commit e7f2be11 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Thomas Gleixner
Browse files

sched/cputime: Fix getrusage(RUSAGE_THREAD) with nohz_full 



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: default avatarHasegawa Hitomi <hasegawa-hitomi@fujitsu.com>
Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarHasegawa Hitomi <hasegawa-hitomi@fujitsu.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarMasayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Acked-by: default avatarPhil Auld <pauld@redhat.com>
Link: https://lore.kernel.org/r/20211026141055.57358-3-frederic@kernel.org
parent d58071a8

include/linux/sched/cputime.h

+3 −2
Original line number Diff line number Diff line
@@ -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)

kernel/sched/cputime.c

+9 −3
Original line number Diff line number Diff line
@@ -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)