Switch pfil(9) to rmlocks

[Max Laier]

On Sunday 25 November 2007, Darren Reed wrote:
> 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%...

Sorry for the sparse explanation.  All numbers above are gain with rmlocks 
i.e. rmlocks are faster in all scenarios.  The test cases are different 
hook functions.  Every hook has a DELAY(1) and a lock/unlock call around 
it of the respective lock type.  read lock acquisitions for rw and rm.  
Please look at the code I posted a bit later for more details.

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