From f7cce27f5605b9e137b829a47949cb2d3c7e1cab Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Mon, 7 Jul 2008 14:16:51 -0400 Subject: [PATCH] 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 Cc: Steven Rostedt Cc: Peter Zijlstra Cc: Andrew Morton Signed-off-by: Ingo Molnar --- kernel/sched_clock.c | 11 +++++++++-- 1 file 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)