On Sat, Jan 13, 2007 at 03:39:45PM +1100, Nick Piggin wrote:
> 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"?
Critical Section :). This is the maximal time interval I measured from
t2 above to the time point we release the spin lock. This is the hold
time I guess.
>
> 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.
The maximal hold time was about 3s.
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