Author: Gian-Carlo Pascutto
Date: 03:27:09 11/01/05
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On November 01, 2005 at 06:17:59, Gabor Szots wrote: >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. No. If task manager shows only 50% of the CPU being used, that means the program is running (flat out) on 1 of the 2 virtual CPUs. However, since there really is only 1 CPU, this means it *is* using the processor to it's full extent. >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. That's what they do. You could see it as your 1x 3.0Ghz CPU pretending it's a 2x 3.0Ghz CPU. If a program uses 1 of those, it'll just use the full CPU. If it uses "both" of them, the real processor has to alternate between the two, running 1 half of the time and the other the other half, so it'll run no faster in the end. The idea behind hyperthreading was that the programs don't really use the CPU fully most of the time, so there is some free time to take advantage of. In reality, most chessprograms are pretty well optimized and the speedup is very small. -- GCP
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