Switch pfil(9) to rmlocks

Darren Reed darrenr at freebsd.org
Sat Nov 24 22:27:30 PST 2007


Max Laier wrote:
> 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
>   

Is that 13%/5%/35% faster or slower or improvement or degradation?
If "rw hook" (using rwlock like we have today?) is 5%, whas is the baseline?

I'm expecting that at least one of these should be a 0%...

Darren



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