Re: Switch pfil(9) to rmlocks

On Saturday 24 November 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!).

attached again text/x-csrc attachment got stripped.

> 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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