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[PATCH 0/7] cputime: A few tickless cputime accounting fixes and improvements

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  [PATCH 0/7] cputime: A few tickless cputime accounting fixes and improvements Frederic Weisbecker <fweisbec@gmail.com> - 2015-11-19 17:00 +0100
    [PATCH 2/7] cputime: Remove extra cost in task_cputime Frederic Weisbecker <fweisbec@gmail.com> - 2015-11-19 17:00 +0100

#1273242 — [PATCH 0/7] cputime: A few tickless cputime accounting fixes and improvements

The first two patches from Hiroshi Shimamoto are fixes to be backported.
Although it's debatable whether the 2nd patch needs backport.

The patches that follow are further fixes and cleanups and the last
one is an optimization.

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	cputime/fixes

HEAD: e4b430e6598cf6e069b08d7a81ee2ca75fe385f2

Thanks,
	Frederic
---

Frederic Weisbecker (5):
      cputime: Clarify vtime symbols and document them
      cputime: Correctly handle task guest time on housekeepers
      cputime: Rename vtime_accounting_enabled to vtime_accounting_cpu_enabled
      cputime: Introduce vtime accounting check for readers
      cputime: Convert vtime_seqlock to seqcount

Hiroshi Shimamoto (2):
      cputime: Fix invalid gtime in proc
      cputime: Remove extra cost in task_cputime


 include/linux/context_tracking.h |  4 +--
 include/linux/init_task.h        |  2 +-
 include/linux/sched.h            |  7 ++--
 include/linux/vtime.h            | 25 ++++++++++----
 kernel/fork.c                    |  4 +--
 kernel/sched/cputime.c           | 75 +++++++++++++++++++++++++---------------
 kernel/time/tick-sched.c         |  2 +-
 7 files changed, 77 insertions(+), 42 deletions(-)
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#1273245 — [PATCH 2/7] cputime: Remove extra cost in task_cputime

From: Hiroshi Shimamoto <h-shimamoto@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-shimamoto@ct.jp.nec.com>
Cc: stable@vger.kernel.org
Cc: Christoph Lameter <cl@linux.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Frederic Weisbecker <fweisbec@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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