Re: hyperthreaded cpu still an issue in 8.4?

From: Jean-David Beyer <jeandavid8(at)verizon(dot)net>
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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
Message-ID: 4A660298.1030300@verizon.net
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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 http://counter.li.org
^^-^^ 13:55:01 up 6 days, 3:52, 3 users, load average: 4.03, 4.25, 4.45

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