From: Hiroshi Shimamoto <h-shimam...@ct.jp.nec.com>
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-shimam...@ct.jp.nec.com>
Cc: sta...@vger.kernel.org
Cc: Christoph Lameter <c...@linux.com>
Cc: Chris Metcalf <cmetc...@ezchip.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Luiz Capitulino <lcapitul...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Rik van Riel <r...@redhat.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Hiroshi Shimamoto <h-shimam...@ct.jp.nec.com>
Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
---
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)
--
2.5.3
--
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