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    SubjectRe: High lock spin time for zone->lru_lock under extreme conditions
    Ravikiran G Thirumalai wrote:
    > Hi,
    > We noticed high interrupt hold off times while running some memory intensive
    > tests on a Sun x4600 8 socket 16 core x86_64 box. We noticed softlockups,

    [...]

    > We did not use any lock debugging options and used plain old rdtsc to
    > measure cycles. (We disable cpu freq scaling in the BIOS). All we did was
    > this:
    >
    > void __lockfunc _spin_lock_irq(spinlock_t *lock)
    > {
    > local_irq_disable();
    > ------------------------> rdtsc(t1);
    > preempt_disable();
    > spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
    > _raw_spin_lock(lock);
    > ------------------------> rdtsc(t2);
    > if (lock->spin_time < (t2 - t1))
    > lock->spin_time = t2 - t1;
    > }
    >
    > On some runs, we found that the zone->lru_lock spun for 33 seconds or more
    > while the maximal CS time was 3 seconds or so.

    What is the "CS time"?

    It would be interesting to know how long the maximal lru_lock *hold* time is,
    which could give us a better indication of whether it is a hardware problem.

    For example, if the maximum hold time is 10ms, that it might indicate a
    hardware fairness problem.

    --
    SUSE Labs, Novell Inc.
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