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>

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 05de80b48586e9fa3241c708c7e6fd7c9b6fb24a..1128d4ba6c552822143e9b1cea0f12d7e6aa8d57 100644 (file)
--- 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)