diff options
| author | Eric Dumazet <eric.dumazet@gmail.com> | 2009-09-30 20:36:19 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-09-30 22:56:10 +0200 |
| commit | 152f9d0710a62708710161bce1b29fa8292c8c11 (patch) | |
| tree | 1a9fb02d236a0328a711eccdef9e29112e216ff7 /kernel/sched_clock.c | |
| parent | 79e1dd05d1a22e95ab6d54d21836f478b3b56976 (diff) | |
| download | lwn-152f9d0710a62708710161bce1b29fa8292c8c11.tar.gz lwn-152f9d0710a62708710161bce1b29fa8292c8c11.zip | |
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@de.ibm.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20090930170754.0886ff2e@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched_clock.c')
| -rw-r--r-- | 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 ac2e1dc708bd..479ce5682d7c 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; |