From: Steven Rostedt <rostedt@goodmis.org>
Date: Wed, 9 Jul 2008 04:15:32 +0000 (-0400)
Subject: sched_clock: record TSC after gtod
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=a83bc47c33ab182f1e48977fd5a04024d713c75e;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git

sched_clock: record TSC after gtod

To read the gtod we need to grab the xtime lock for read. Reading the gtod
before the TSC can cause a bigger gab if the xtime lock is contended.

This patch simply reverses the order to read the TSC after the gtod.
The locking in the reading of the gtod handles any barriers one might
think is needed.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index ee7cce5029c..28ff6bf5e02 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -237,8 +237,8 @@ void sched_clock_tick(void)
 
 	WARN_ON_ONCE(!irqs_disabled());
 
-	now = sched_clock();
 	now_gtod = ktime_to_ns(ktime_get());
+	now = sched_clock();
 
 	__raw_spin_lock(&scd->lock);
 	__update_sched_clock(scd, now, NULL);