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Re: hyperthreaded cpu still an issue in 8.4?

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Matthew Wakeling <matthew(at)flymine(dot)org>
Cc: Dave Youatt <dave(at)meteorsolutions(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: hyperthreaded cpu still an issue in 8.4?
Date: 2009-07-28 20:28:24
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Lists: pgsql-performance
On Tue, 28 Jul 2009, Matthew Wakeling wrote:

> Unlikely. Different threads on the same CPU core share their resources, so 
> they don't need an explicit communication channel at all (I'm simplifying 
> massively here). A real interconnect is only needed between CPUs and between 
> different cores on a CPU, and of course to the outside world.

The question was "why are the new CPUs benchmarking so much faster than 
the old ones", and I believe that's mainly because the interconnection 
both between CPUs and between CPUs and memory are dramatically faster. 
The SMT improvements stack on top of that, but are in my opinion 
secondary.  I base that on also seeing a dramatic improvement in memory 
transfer speeds on the new platform, which alone might even be sufficient 
to explain the performance boost.  I'll break the two factors apart later 
to be sure though--all the regulars on this list know where I stand on 
measuring performance compared with theorizing about it.

* Greg Smith gsmith(at)gregsmith(dot)com Baltimore, MD

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