Commit-ID: 623c4f89c47cca0088014388211d8bc0a5358f0a Gitweb: http://git.kernel.org/tip/623c4f89c47cca0088014388211d8bc0a5358f0a Author: Eric Dumazet <eric.dumazet@xxxxxxxxx> AuthorDate: Wed, 30 Sep 2009 20:36:19 +0200 Committer: Ingo Molnar <mingo@xxxxxxx> CommitDate: Wed, 30 Sep 2009 22:36:12 +0200 sched_clock: Fix atomicity/continuity bug by using cmpxchg64() Commit def0a9b2573 (sched_clock: Make it NMI safe) assumed cmpxchg() of 64bit values was available on X86_32. That is not so - and causes some subtle scheduler misbehavior due to incorrect timestamps off to up by ~4 seconds. Two symptoms are known right now: - interactivity problems seen by Arjan: up to 600 msecs latencies instead of the expected 20-40 msecs. These latencies are very visible on the desktop. - incorrect CPU stats: occasionally too high percentages in 'top', and crazy CPU usage stats. Reported-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx> Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: John Stultz <johnstul@xxxxxxxxxx> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> LKML-Reference: <20090930170754.0886ff2e@xxxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxx> --- kernel/sched_clock.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index ac2e1dc..479ce56 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -127,7 +127,7 @@ again: clock = wrap_max(clock, min_clock); clock = wrap_min(clock, max_clock); - if (cmpxchg(&scd->clock, old_clock, clock) != old_clock) + if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock) goto again; return clock; @@ -163,7 +163,7 @@ again: val = remote_clock; } - if (cmpxchg(ptr, old_val, val) != old_val) + if (cmpxchg64(ptr, old_val, val) != old_val) goto again; return val; -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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