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 --- kernel/sched_clock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux-tip.git/kernel/sched_clock.c =================================================================== --- linux-tip.git.orig/kernel/sched_clock.c 2008-07-08 11:03:05.000000000 -0400 +++ linux-tip.git/kernel/sched_clock.c 2008-07-08 16:53:34.000000000 -0400 @@ -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); -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/