I know that ESX(i) has a setting that allows you to take advantage of
hyperthreading if it's enabled in the bios. I haven't done any tests
to determine if it actually improves performance or not, but since
there's a setting for it, I'm blindly guessing that it doesn't hurt
(assuming you have the little box checked)

--Matt


On Wed, Jul 21, 2010 at 2:01 PM, Doug Hughes <[email protected]> wrote:
> Yves Dorfsman wrote:
>> On 10-07-21 11:30 AM, Doug Hughes wrote:
>>
>>> Yves Dorfsman wrote:
>>>
>>>> I know that disabling hyper-threading in the BIOS improves performance
>>>> for some type of applications.
>>>>
>>>> Has anybody looked into, or has experience the impact of disabling VT
>>>> and VT-d on performance?
>>>>
>>>>
>>
>>
>>> It depends greatly upon the application. Some multi-threaded
>>> applications get boost from having it enabled as it helps with hardware
>>> context switching. Single-threaded monolithic applications can benefit
>>> by not having this on and having one per core. There are many other
>>> factors including whether the application fits in cache that affect
>>> performance too.
>>>
>>
>> Are you talking about hyper-threading or VT / VT-d here?
>>
>> For hyper-threading, the software vendor is recommending to disable it, based
>> on their own tests.
>>
>> (btw, in case it isn't obvious, I am talking about systems dedicated to one 
>> OS
>> install only (the old fashion way), rather than VMs, or VM monitors).
>>
>>
> I was talking about hyperthreading, but it also applies to a more
> limited extent to virtualization technology. If you're not running or
> planning on running virtualization, you may or may not get a performance
> boost out of disabling it, and it's probably dependent on several factors.
>
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