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Subject: Re: Hyperthreading - with half speed?

Author: Gabor Szots

Date: 03:17:59 11/01/05

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On November 01, 2005 at 05:58:14, Gian-Carlo Pascutto wrote:

>On November 01, 2005 at 05:44:34, Gabor Szots wrote:
>
>>I just got a new machine with P4 3GHz CPU. Analyzing positons with chess
>>programs I looked at task manager and was surprised by seeing that only 50% CPU
>>was assigned to the chess program thread while the other 50% was idle.
>>I tried the same with Deep Sjeng with 2 processor setting and I saw 2 50% CPU
>>threads while the system was idle 0%. Ok, however the Nps was the same as with
>>only 1 processor, and test solution times were also the same.
>>This all was under WinXP SP2.
>>
>>How can I exploit full CPU power? Any explanation would be welcome.
>
>A system with hyperthreading really only has a single processor, it just
>pretends there are two. At best you will get a few percent speedup.
>
>A real dual core processor will give >70-80% speedup.
>
>--
>GCP

The problem is that the system behaves as though the CPU ran at only 1.5 Ghz
instead of 3. If there is only 1 thread, why do the chess programs not use
'both' CPU's? I think both halves of the CPU should process that single thread
simultaneously, thereby adding their 1.5 Ghz speeds together.
I have a feeling that I don't understand this at all. I don't want a speedup, I
would like to avoid a slowdown.



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