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On Friday 23 November 2007, Robert Watson wrote:
> On Fri, 23 Nov 2007, Max Laier wrote:
> > attached is a diff to switch the pfil(9) subsystem to rmlocks, which
> > are more suited for the task. I'd like some exposure before doing
> > the switch, but I don't expect any fallout. This email is going
> > through the patched pfil already - twice.

> Max,
> Have you done performance measurements that show rmlocks to be a win in
> this scenario? I did some patchs for UNIX domain sockets to replace
> the rwlock there but it appeared not to have a measurable impact on SQL
> benchmarks, presumbaly because the read/write blend wasn't right and/or
> that wasnt a significant source of overhead in the benchmark. I'd
> anticipate a much more measurable improvement for pfil, but would be
> interested in learning how much is seen?

I had to roll an artificial benchmark in order to see a significant change=
(attached - it's a hack!).

Using 3 threads on a 4 CPU machine I get the following results:
null hook: ~13% +/- 2
mtx hook: up to 40%[*]
rw hook: ~5% +/- 1
rm hook: ~35% +/- 5
[*] The mtx hook is inconclusive as my measurements vary a lot. If one=20
thread gets lucky and keeps running the overall time obviously goes down=20
by a magnitude. It seems however, that rmlocks greatly increase the=20
chance of that happening - not sure if that's a good thing, though. If=20
all threads receive approximately equal runtime (which is almost always=20
the case for rwlocks) the difference is somewhere around 10%.

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