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Re: Large (8M) cache vs. dual-core CPUs

From: mark(at)mark(dot)mielke(dot)cc
To: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
Cc: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>,Scott Marlowe <smarlowe(at)g2switchworks(dot)com>,Bill Moran <wmoran(at)collaborativefusion(dot)com>,pgsql-performance(at)postgresql(dot)org
Subject: Re: Large (8M) cache vs. dual-core CPUs
Date: 2006-04-27 02:56:02
Message-ID: 20060427025602.GA19089@mark.mielke.cc (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, Apr 26, 2006 at 05:37:31PM -0500, Jim C. Nasby wrote:
> On Wed, Apr 26, 2006 at 06:16:46PM -0400, Bruce Momjian wrote:
> > AMD transfers the dirty cache line directly from cpu to cpu.  I can
> > imaging that helping our test-and-set shared memory usage quite a bit.
> Wasn't the whole point of test-and-set that it's the recommended way to
> do lightweight spinlocks according to AMD/Intel? You'd think they'd have
> a way to make that performant on multiple CPUs (though if it's relying
> on possibly modifying an underlying data page I can't really think of
> how to do that without snaking through the cache...)

It's expensive no matter what. One method might be less expensive than
another. :-)

AMD definately seems to have things right for lowest absolute latency.
2X still sounds like an extreme case - but until I've actually tried a
very large, or thread intensive PostgreSQL db on both, I probably
shouldn't doubt the work of others too much. :-)

Cheers,
mark

-- 
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