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Re: hyperthreaded cpu still an issue in 8.4?

From: Jon Nelson <jnelson(at)jamponi(dot)net>
To:
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: hyperthreaded cpu still an issue in 8.4?
Date: 2009-07-28 21:45:51
Message-ID: cccedfc60907281445r6e719b48v6a26cd8ab2a8eb4b@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Tue, Jul 28, 2009 at 4:11 PM, Scott Marlowe<scott(dot)marlowe(at)gmail(dot)com> wrote:
> On Tue, Jul 28, 2009 at 2:58 PM, Merlin Moncure<mmoncure(at)gmail(dot)com> wrote:
>> On Mon, Jul 27, 2009 at 2:05 PM, Dave Youatt<dave(at)meteorsolutions(dot)com> wrote:
>>> On 01/-10/-28163 11:59 AM, Greg Smith wrote:
>>>> On Tue, 21 Jul 2009, Doug Hunley wrote:
>>>>
>>>>> Just wondering is the issue referenced in
>>>>> http://archives.postgresql.org/pgsql-performance/2005-11/msg00415.php
>>>>> is still present in 8.4 or if some tunable (or other) made the use of
>>>>> hyperthreading a non-issue. We're looking to upgrade our servers soon
>>>>> for performance reasons and am trying to determine if more cpus (no
>>>>> HT) or less cpus (with HT) are the way to go.
>>>>
>>>> If you're talking about the hyperthreading in the latest Intel Nehalem
>>>> processors, I've been seeing great PostgreSQL performance from those.
>>>> The kind of weird behavior the old generation hyperthreading designs
>>>> had seems gone.  You can see at
>>>> http://archives.postgresql.org/message-id/alpine.GSO.2.01.0907222158050.16713@westnet.com
>>>> that I've cleared 90K TPS on a 16 core system (2 quad-core
>>>> hyperthreaded processors) running a small test using lots of parallel
>>>> SELECTs.  That would not be possible if there were HT spinlock
>>>> problems still around. There have been both PostgreSQL scaling
>>>> improvments and hardware improvements since the 2005 messages you saw
>>>> there that have combined to clear up the issues there.  While true
>>>> cores would still be better if everything else were equal, it rarely
>>>> is, and I wouldn't hestitate to jump on Intel's bandwagon right now.
>>>
>>> Greg, those are compelling numbers for the new Nehalem processors.
>>> Great news for postgresql.  Do you think it's due to the new internal
>>> interconnect, that bears a strong resemblance to AMD's hypertransport

I'd love to see some comparisons on the exact same hardware, same
kernel and everything but with HT enabled and disabled. Don't forget
that newer (Linux) kernels have vastly improved SMP performance.

-- 
Jon

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