| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Andrea Suisani <sickpig(at)opinioni(dot)net> |
| Cc: | Craig James <cjames(at)emolecules(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Two identical systems, radically different performance |
| Date: | 2012-10-11 14:19:33 |
| Message-ID: | CAGTBQpYGyq70q_S_dUngSwB7yLbbCxetnfXpaMC9LEr7zL6iWA@mail.gmail.com |
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| Lists: | pgsql-performance |
On Thu, Oct 11, 2012 at 11:14 AM, Andrea Suisani <sickpig(at)opinioni(dot)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?
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.
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