Re: 67-mjb2 vs 68-mjb1 (sdet degredation)

[Martin J. Bligh]

>> > Here's a backout patch.  Does it fix it up?
>> 
>> Yeah, that fixes it. Ho hum ... I wonder if we can find something that
>> works well for both cases? I guess the options would be:
>> 
>> 1. Some way to make the rwlock mechanism itself faster.
>> 2. Try to fix the contention itself somehow for this instance.
> 
> You're using PIII's, which don't mind the additional buslocked operation. 
> P4's hate it.  We'd need to retest on big P4 and other architectures to
> decide.

OK, I can try do get someone to test on big x440s (P4 Xeon).
 
> I suspect the spinlock is better that the rwlock overall - having multiple
> CPUs looking up things in the same address_space is relatively uncommon. 
> Having one CPU looking things up in one address space is very common, and
> that's the thing which the s/rwlock/spinlock/ speeds up.

Yeah, wasn't really complaining - I think the spinlock is the right thing
to do ... I just wanted to nail down what caused it, and be sure it was
deliberate. Looks like it is, so that all seems OK. Thanks for the help ;-)

M.