Commit 7877a0ba authored Nov 19, 2015 by Hiroshi Shimamoto Committed by Ingo Molnar Dec 04, 2015

sched/cputime: Remove extra cost in task_cputime()



There is an extra cost in task_cputime() and task_cputime_scaled() when
nohz_full is not activated. When vtime accounting is not enabled, we
don't need to get deltas of utime and stime under vtime seqlock.

This patch removes that cost with adding a shortcut route if vtime
accounting is not enabled.

Use context_tracking_is_enabled() to check if vtime is accounting on
some cpu, in which case only we need to check the tickless cputime delta.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1447948054-28668-3-git-send-email-fweisbec@gmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent ad936d86

kernel/sched/cputime.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -853,6 +853,14 @@ void task_cputime(struct task_struct t, cputime_t utime, cputime_t *stime)
		{
		cputime_t udelta, sdelta;

		if (!context_tracking_is_enabled()) {
		if (utime)
		*utime = t->utime;
		if (stime)
		*stime = t->stime;
		return;
		}

		fetch_task_cputime(t, utime, stime, &t->utime,
		&t->stime, &udelta, &sdelta);
		if (utime)
		@@ -866,6 +874,14 @@ void task_cputime_scaled(struct task_struct *t,
		{
		cputime_t udelta, sdelta;

		if (!context_tracking_is_enabled()) {
		if (utimescaled)
		*utimescaled = t->utimescaled;
		if (stimescaled)
		*stimescaled = t->stimescaled;
		return;
		}

		fetch_task_cputime(t, utimescaled, stimescaled,
		&t->utimescaled, &t->stimescaled, &udelta, &sdelta);
		if (utimescaled)

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