Re: Linux: more cores = less concurrency.

On Mon, Apr 11, 2011 at 12:23 PM, Glyn Astill <glynastill(at)yahoo(dot)co(dot)uk> wrote:
>
>
> --- On Mon, 11/4/11, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
>
>> From: Joshua D. Drake <jd(at)commandprompt(dot)com>
>> Subject: Re: [PERFORM] Linux: more cores = less concurrency.
>> To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
>> Cc: pgsql-performance(at)postgresql(dot)org, "Glyn Astill" <glynastill(at)yahoo(dot)co(dot)uk>
>> Date: Monday, 11 April, 2011, 19:12
>> On Mon, 11 Apr 2011 13:09:15 -0500,
>> "Kevin Grittner"
>> <Kevin(dot)Grittner(at)wicourts(dot)gov>
>> wrote:
>> > Glyn Astill <glynastill(at)yahoo(dot)co(dot)uk>
>> wrote:
>> >
>> >> The new server uses 4 x 8 core Xeon X7550 CPUs at
>> 2Ghz
>> >
>> > Which has hyperthreading.
>> >
>> >> our current servers are 2 x 4 core Xeon E5320 CPUs
>> at 2Ghz.
>> >
>> > Which doesn't have hyperthreading.
>> >
>
> Yep, off. If you look at the benchmarks I took, HT absoloutely killed it.
>
>> > PostgreSQL often performs worse with hyperthreading
>> than without.
>> > Have you turned HT off on your new machine?  If
>> not, I would start
>> > there.
>>
>> And then make sure you aren't running CFQ.
>>
>> JD
>>
>
> Not running CFQ, running the no-op i/o scheduler.

Just FYI, in synthetic pgbench type benchmarks, a 48 core AMD Magny
Cours with LSI HW RAID and 34 15k6 Hard drives scales almost linearly
up to 48 or so threads, getting into the 7000+ tps range. With SW
RAID it gets into the 5500 tps range.