linux-kernel - [tip:sched/core] sched/cputime: Remove extra cost in task

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Date:	Fri, 4 Dec 2015 03:55:09 -0800
From:	tip-bot for Hiroshi Shimamoto <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	riel@...hat.com, mingo@...nel.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	h-shimamoto@...jp.nec.com, lcapitulino@...hat.com,
	paulmck@...ux.vnet.ibm.com, efault@....de, cmetcalf@...hip.com,
	fweisbec@...il.com, torvalds@...ux-foundation.org, cl@...ux.com,
	peterz@...radead.org
Subject: [tip:sched/core] sched/cputime: Remove extra cost in task_cputime
 ()

Commit-ID:  7877a0ba5ec63c7b0111b06c773f1696fa17b35a
Gitweb:     http://git.kernel.org/tip/7877a0ba5ec63c7b0111b06c773f1696fa17b35a
Author:     Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
AuthorDate: Thu, 19 Nov 2015 16:47:29 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 4 Dec 2015 10:34:43 +0100

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@...jp.nec.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Chris Metcalf <cmetcalf@...hip.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Mike Galbraith <efault@....de>
Cc: Paul E . McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1447948054-28668-3-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/cputime.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 05de80b..1128d4b 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -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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