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authorSteven Rostedt <rostedt@goodmis.org>2008-07-07 20:16:51 +0200
committerIngo Molnar <mingo@elte.hu>2008-07-11 15:53:25 +0200
commitf7cce27f5605b9e137b829a47949cb2d3c7e1cab (patch)
treefbe270ccfb5cee3d055a52b6351ade2d34c5d74b /kernel/sched_clock.c
parentsched_clock: record from last tick (diff)
downloadlinux-f7cce27f5605b9e137b829a47949cb2d3c7e1cab.tar.xz
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sched_clock: widen the max and min time
With keeping the max and min sched time within one jiffy of the gtod clock was too tight. Just before a schedule tick the max could easily be hit, as well as just after a schedule_tick the min could be hit. This caused the clock to jump around by a jiffy. This patch widens the minimum to last gtod + (delta_jiffies ? delta_jiffies - 1 : 0) * TICK_NSECS and the maximum to last gtod + (2 + delta_jiffies) * TICK_NSECS This keeps the minum to gtod or if one jiffy less than delta jiffies and the maxim 2 jiffies ahead of gtod. This may cause unstable TSCs to be a bit more sporadic, but it helps keep a clock with a stable TSC working well. 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> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched_clock.c')
-rw-r--r--kernel/sched_clock.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index e383bc7df6dd..42b81fa38cbd 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -96,14 +96,21 @@ static void __update_sched_clock(struct sched_clock_data *scd, u64 now)
s64 delta = now - scd->prev_raw;
WARN_ON_ONCE(!irqs_disabled());
- min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC;
+
+ min_clock = scd->tick_gtod +
+ (delta_jiffies ? delta_jiffies - 1 : 0) * TICK_NSEC;
if (unlikely(delta < 0)) {
clock++;
goto out;
}
- max_clock = min_clock + TICK_NSEC;
+ /*
+ * The clock must stay within a jiffie of the gtod.
+ * But since we may be at the start of a jiffy or the end of one
+ * we add another jiffy buffer.
+ */
+ max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
if (unlikely(clock + delta > max_clock)) {
if (clock < max_clock)