Switch pfil(9) to rmlocks

Max Laier max at love2party.net
Fri Nov 23 05:42:49 PST 2007

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 don't yet, but will see if I can collect some data later today.  The 
main reason for the switch is shortcomings in rwlock's (not) 
implementation of reader recursion as discussed in -arch "rwlocks, 
correctness over speed."  rmlocks do that correctly, afaiu.

Unless an artificial no-op hook is used, I don't expect to see significant 
performance gain, however.  All current pfil(9) consumer need some form 
of synchronization of their own, which will probably nullify the gain 
from rmlocks.

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