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authorEric Dumazet <eric.dumazet@gmail.com>2009-09-30 20:36:19 +0200
committerIngo Molnar <mingo@elte.hu>2009-09-30 22:56:10 +0200
commit152f9d0710a62708710161bce1b29fa8292c8c11 (patch)
tree1a9fb02d236a0328a711eccdef9e29112e216ff7 /Documentation/DocBook
parent79e1dd05d1a22e95ab6d54d21836f478b3b56976 (diff)
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>
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