Hypertherading

[Olivier SMEDTS]

2009/5/7 Barney Cordoba <barney_cordoba at yahoo.com>:
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> --- On Wed, 5/6/09, pluknet <pluknet at gmail.com> wrote:
>
>> From: pluknet <pluknet at gmail.com>
>> Subject: Re: Hypertherading
>> To: "Barney Cordoba" <barney_cordoba at yahoo.com>
>> Cc: "Current at freebsd.org" <Current at freebsd.org>
>> Date: Wednesday, May 6, 2009, 10:55 PM
>> 2009/5/7 Barney Cordoba <barney_cordoba at yahoo.com>:
>> >
>> > I just got a shiny new nehalem box and it comes up
>> with 16 processors with dual quads installed. Is there any
>> benefit or should hyperthreading be disabled?

There can be some benefit if the scheduler is aware of the topoly of
CPUs and Hyperthreading (shared cache). I don't know how SCHED_ULE
handles this on -CURRENT. If it doesn't see any difference between CPU
cores and "HT" cores, you should disable HT in BIOS.

>> >
>>
>> Hi. There is a measurable win if hyperthreading is enabled
>> [1].
>> You can switch it off via machdep.hyperthreading_enabled
>> loader tunable.
>>
>> [1]
>> http://lists.freebsd.org/pipermail/freebsd-stable/2009-January/047460.html
>>
>
> I wouldn't call varying the number of jobs a very good test
> of hyperthreading. I'd want to see the exact same test with
> hyperthreading enabled and disabled. Its pretty naive
> to assume that running 16 jobs causes them to all be run on
> a different cpu.
>
> Barney
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-- 
Olivier Smedts                                                 _
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