Re: Some interesting results from tweaking spinlocks

The number of CPUs on a system should be fairly straight forward to
find out. Distributed.net source code has some good examples.

What I'm not sure of is how well this stuff reacts to CPUs being
software disabled (Solaris has such a feature).

ftp://ftp.distributed.net/pub/dcti/source/pub-20010416.tgz

first function of client/common/cpucheck.cpp

Each OS gets its own implementation, but they've got all the ones
Postgresql uses covered off.
--
Rod Taylor

This message represents the official view of the voices in my head

----- Original Message -----
From: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Bruce Momjian" <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Sent: Friday, January 04, 2002 11:49 PM
Subject: Re: [HACKERS] Some interesting results from tweaking
spinlocks

> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > The difference is small, perhaps 15%.
>
> The thing that gets my attention is not that it's so small, it's
that
> it is so large. My expectation was that that code would hardly ever
> be executed at all, and even less seldom (on a multiprocessor) need
to
> block via select(). How is it that *increasing* the delay interval
> (which one might reasonably expect to simply waste cycles) can
achieve
> a 15% improvement in total throughput? That shouldn't be happening.
>
> > My feeling is that we may want to start configuring whether we are
on
> > a multi-cpu machine and handle thing differently.
>
> That would be more palatable if there were some portable way of
> detecting it. But maybe we'll be forced into an "is_smp" GUC
switch.
>
> regards, tom lane
>
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