Re: Switch pfil(9) to rmlocks

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
thread gets lucky and keeps running the overall time obviously goes down
by a magnitude. It seems however, that rmlocks greatly increase the
chance of that happening - not sure if that's a good thing, though. If
all threads receive approximately equal runtime (which is almost always
the case for rwlocks) the difference is somewhere around 10%.

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Relevant Pages

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