Re: Spinlocks, yet again: analysis and proposed patches

On Wed, 2005-10-19 at 14:07 -0700, Mark Wong wrote:
> >
> > This isn't exactly elegant coding, but it provides a useful improvement
> > on an 8-way SMP box when run on 8.0 base. OK, lets be brutal: this looks
> > pretty darn stupid. But it does follow the CPU optimization handbook
> > advice and I did see a noticeable improvement in performance and a
> > reduction in context switching.

> > I'm not in a position to try this again now on 8.1beta, but I'd welcome
> > a performance test result from anybody that is. I'll supply a patch
> > against 8.1beta for anyone wanting to test this.
>
> Ok, I've produce a few results on a 4 way (8 core) POWER 5 system, which
> I've just set up and probably needs a bit of tuning. I don't see much
> difference but I'm wondering if the cacheline sizes are dramatically
> different from Intel/AMD processors. I still need to take a closer look
> to make sure I haven't grossly mistuned anything, but I'll let everyone
> take a look:

Well, the Power 5 architecture probably has the lowest overall memory
delay you can get currently so in some ways that would negate the
effects of the patch. (Cacheline is still 128 bytes, AFAICS). But it's
clear the patch isn't significantly better (like it was with 8.0 when we
tried this on the 8-way Itanium in Feb).

> cvs 20051013
> http://www.testing.osdl.org/projects/dbt2dev/results/dev4-014/19/
> 2501 notpm
>
> cvs 20051013 w/ lw.patch
> http://www.testing.osdl.org/projects/dbt2dev/results/dev4-014/20/
> 2519 notpm

Could you re-run with wal_buffers = 32 ? (Without patch) Thanks

Best Regards, Simon Riggs