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Re: hyperthreaded cpu still an issue in 8.4?

From: Jean-David Beyer <jeandavid8(at)verizon(dot)net>
Cc: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: hyperthreaded cpu still an issue in 8.4?
Date: 2009-07-21 18:02:00
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Lists: pgsql-performance
Scott Carey wrote:
> But back on topic for HT -- HT doesn't like spin-locks much unless they
> use the right low level instruction sequence rather than actually
> spinning. With the right instruction, the spin will allow the other
> thread to do work... With the wrong one, it will tie up the pipeline.  I
> have no idea what Postgres' spin-locks and tool chain compile down to.
I have two hyperthreaded Xeon processors, so this machine thinks it has four 
processors. I have not seen the effect of spin locks with postgres. But I 
can tell that Firefox and Thunderbird use the wrong ones. When one of these 
is having trouble accessing a site, the processor in question goes up to 
100% and the other part of the hyperthreaded processor does nothing even 
though I run four BOINC processes that would be glad to gobble up the 
cycles. Of course, since it is common to both Firefox and Thunderbird, 
perhaps it is a problem in the name server, bind. But wherever it is, it 
bugs me.

   .~.  Jean-David Beyer          Registered Linux User 85642.
   /V\  PGP-Key: 9A2FC99A         Registered Machine   241939.
  /( )\ Shrewsbury, New Jersey
  ^^-^^ 13:55:01 up 6 days, 3:52, 3 users, load average: 4.03, 4.25, 4.45

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