From: Andrea Suisani <sickpig@opinioni.net>
To: Claudio Freire <klaussfreire@gmail.com>
Cc: Craig James <cjames@emolecules.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Two identical systems, radically different performance
Date: Thu, 11 Oct 2012 16:40:14 +0200
Message-ID: <5076DA4E.80504@opinioni.net> (raw)
In-Reply-To: <CAGTBQpYGyq70q_S_dUngSwB7yLbbCxetnfXpaMC9LEr7zL6iWA@mail.gmail.com>
References: <CAFwQ8rcvw4mSoJ9q+ouONCeB9dg1T9gAUV5J27MpVZrehRHayQ@mail.gmail.com>
<CAFwQ8rfm2AcuoFHDfBLA_hg7ffbsYNsrsaJPDqcOeGqaVW02OQ@mail.gmail.com>
<CAFwQ8rcyCKcoeEn62_QHMRSmJM03ULERtW6_R=3TaO0twOEV9A@mail.gmail.com>
<5076D433.7090605@opinioni.net>
<CAGTBQpYGyq70q_S_dUngSwB7yLbbCxetnfXpaMC9LEr7zL6iWA@mail.gmail.com>
On 10/11/2012 04:19 PM, Claudio Freire wrote:
> On Thu, Oct 11, 2012 at 11:14 AM, Andrea Suisani <sickpig@opinioni.net> wrote:
>> sorry to come late to the party, but being in a similar condition
>> I've googled a bit and I've found a way to disable hyperthreading without
>> the need to reboot the system and entering the bios:
>>
>> echo 0 >/sys/devices/system/node/node0/cpuX/online
>>
>> where X belongs to 1..(#cores * 2) if hyperthreading is enabled
>> (cpu0 can't be switched off).
>>
>> didn't try myself on live system, but I definitely will
>> as soon as I have a new machine to test.
>
> Question is... will that remove the performance penalty of HyperThreading?
So I've added to my todo list to perform a test to verify this claim :)
> I don't think so, because a big one is the register file split (half
> the hardware registers go to a CPU, half to the other). If that action
> doesn't tell the CPU to "unsplit", some shared components may become
> unbogged, like the decode stage probably, but I'm not sure it's the
> same as disabling it from the BIOS.
Although I think that you're probably right to assume that disabling HT
through the syfs interface won't remove the performance penalty for real.
thanks
Andrea
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: sickpig@opinioni.net, klaussfreire@gmail.com, cjames@emolecules.com
Subject: Re: Two identical systems, radically different performance
In-Reply-To: <5076DA4E.80504@opinioni.net>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox