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From: Julian Elischer <julian@elischer.org>
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To: Evren Yurtesen <yurtesen@ispro.net.tr>
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cc: Vlad <marchenko@gmail.com>
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Subject: Re: panic: sorele
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Evren Yurtesen wrote:
> 
> 
> Vlad wrote:
> 
>> based on your kernel panic:
>>
>>
>>>> panic: sorele
>>>> cpuid = 1
>>>> boot() called on cpu#1
>>>> Uptime: 5d19h48m4s
>>
>>
>>
>> it looks like you do have at least two CPUs... cpu#1 is a second CPU,
>> or I'm mistaken?
>>
> 
> Like I said, it is this hyperthreading from intel. Look from google for 
> hyperthreading. It is suppose to improve performance but who knows...
> 
> -e-
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All our tests so far have shown Hyperthreading reduces performance except in 
some special cases.

the special case where I have seen improved performance is an app where there 
are 2 threads (or processes) where one is doing integer work and the other is 
doing floating point work.
I saw the equivalent of 1.8 CPUs with that load. other standard tests
have however showed a solid decrease in performance in enabling hyperthreading.
Linux machines we have tested also managed to not get any real advantage
from Hyperthreading hoever they somehow managed to at least avoid the DECREASE
with special scheduling code.. Our answer has been to keep HTT turned off unless 
the workload can use it.

In this case "We/our" refers to FreeBSD developers chatting on IRC.