On Tue, Jan 29, 2013 at 09:44:00AM +0100, Ingo Molnar wrote:
>
> * Yuanhan Liu <yuanhan....@linux.intel.com> wrote:
>
> > [...]
>
> Very nice measurements and analysis, thanks!
>
> > As stated above, anybody can have a chance to own the lock in
> > mutex once somebody release the lock. Well, there is only one
> > to own the lock in rwsem write lock, and the one is known
> > already: the one in the head of wait list. That would result
> > to more contention in rwsem write lock case, especially if the
> > one _will_ own the lock is not running now.
>
> I think we should allow lock-steal between rwsem writers - that
> will not hurt fairness as most rwsem fairness concerns relate to
> reader vs. writer fairness.
Agreed, and I'm sure this will improve performance and may make this
performance regression go away.
David, is that Ok to you? If so, I may have a try.
>
> Am I correct to assume that all relevant users in this workload
> are down_write() users?
Yes, as commit 5a50508 just convert all mutex to down_write.
Thanks.
--yliu
>
> You can see the type of lock use in:
>
> perf record -g
> perf report
>
> I bet that allowing rwsem writer lock-steal would improve other
> workloads as well.
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