From e592539466380279a9e6e6fdfe4545aa54f22593 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <fweisbec@gmail.com>
Date: Thu, 19 Nov 2015 16:47:33 +0100
Subject: [PATCH] sched/cputime: Introduce vtime accounting check for readers

Readers need to know if vtime runs at all on some CPU somewhere, this
is a fast-path check to determine if we need to check further the need
to add up any tickless cputime delta.

This fast path check uses context tracking state because vtime is tied
to context tracking as of now. This check appears to be confusing though
so lets use a vtime function that deals with context tracking details
in vtime implementation instead.

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: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.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/1447948054-28668-7-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/vtime.h  | 13 ++++++++++++-
 kernel/sched/cputime.c |  6 +++---
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/vtime.h b/include/linux/vtime.h
index ca23e8348f70..fa2196990f84 100644
--- a/include/linux/vtime.h
+++ b/include/linux/vtime.h
@@ -17,9 +17,20 @@ static inline bool vtime_accounting_cpu_enabled(void) { return true; }
 #endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+/*
+ * Checks if vtime is enabled on some CPU. Cputime readers want to be careful
+ * in that case and compute the tickless cputime.
+ * For now vtime state is tied to context tracking. We might want to decouple
+ * those later if necessary.
+ */
+static inline bool vtime_accounting_enabled(void)
+{
+	return context_tracking_is_enabled();
+}
+
 static inline bool vtime_accounting_cpu_enabled(void)
 {
-	if (context_tracking_is_enabled()) {
+	if (vtime_accounting_enabled()) {
 		if (context_tracking_cpu_is_enabled())
 			return true;
 	}
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 572721756359..9989c3f61723 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -788,7 +788,7 @@ cputime_t task_gtime(struct task_struct *t)
 	unsigned int seq;
 	cputime_t gtime;
 
-	if (!context_tracking_is_enabled())
+	if (!vtime_accounting_enabled())
 		return t->gtime;
 
 	do {
@@ -853,7 +853,7 @@ void task_cputime(struct task_struct *t, cputime_t *utime, cputime_t *stime)
 {
 	cputime_t udelta, sdelta;
 
-	if (!context_tracking_is_enabled()) {
+	if (!vtime_accounting_enabled()) {
 		if (utime)
 			*utime = t->utime;
 		if (stime)
@@ -874,7 +874,7 @@ void task_cputime_scaled(struct task_struct *t,
 {
 	cputime_t udelta, sdelta;
 
-	if (!context_tracking_is_enabled()) {
+	if (!vtime_accounting_enabled()) {
 		if (utimescaled)
 			*utimescaled = t->utimescaled;
 		if (stimescaled)