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From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
To: Josh Berkus <josh@agliodbs.com>
To: Andres Freund <andres@2ndquadrant.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: pgsql-performance@postgresql.org, "Graeme B. Bell" <grb@skogoglandskap.no>
Subject: Re: Turn off Hyperthreading! WAS: 60 core performance with 9.3
Date: Tue, 26 Aug 2014 14:03:53 +1200
Message-ID: <53FBEB09.1050706@catalyst.net.nz> (raw)
In-Reply-To: <53FBB527.9030007@agliodbs.com>
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On 26/08/14 10:13, Josh Berkus wrote:
> On 08/22/2014 07:02 AM, Andres Freund wrote:
>> On 2014-08-21 14:02:26 -0700, Josh Berkus wrote:
>>> On 08/20/2014 07:40 PM, Bruce Momjian wrote:
>>>> Not sure how you can make such a blanket statement when so many people
>>>> have tested and shown the benefits of hyper-threading.
>>>
>>> Actually, I don't know that anyone has posted the benefits of HT.
>>> Link?
>>
>> There's definitely cases where it can help. But it's highly workload
>> *and* hardware dependent.
>
> The only cases I've seen where HT can be beneficial is when you have
> large numbers of idle connections.  Then the idle connections can be
> "parked" on the HT virtual cores.  However, even in this case I haven't
> seen a head-to-head performance comparison.
>

I recall HT beneficial on a single socket (i3 or i7), using pgbench as 
the measuring tool. However I didn't save the results at the time. I've 
just got some new ssd's to play with so might run some pgbench tests on 
my home machine (Haswell i7) with HT on and off.

Regards

Mark


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