Author: Frank Quisinsky
Date: 14:21:18 01/14/04
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On January 14, 2004 at 17:00:49, Thomas Mayer wrote: >Hi Frank, > >seems that you haven't followed the discussion about hyperthreading lately. >Well, I am no real expert in it, but some explanations: Have the possibility to test different boards, processors and so on! The Tyan board is very new and interesting for my network! Yes, I have read some discuss about it but not all, sorry! In the last months I have a lot of work with different things! I will search in CCC for more information about this topic! >First of all: usually nps goes up by a factor of 2 on 2 processors - that is >usual. But they produce some overhead so that a speedup of 1.7-1.8 is a good >guess. (Some stated that they have above 2 - but I would say that sounds like >phantasy... :) >But we compare nps here, so: >2 threads on a Dual with hyperthreading DEACTIVATED (!) gets about double the >nps then 1 thread on the same machine. >When hyperthreadings is activated this is no longer true. Why ? Simple: it's >always unclear on which processor a thread is running - that is also changing >while it is running... so sometimes both threads run on the two virtual >processors of one processor - it's clear that it is slower then. So running an >engine with two threads on a Dual with hyperthreading enabled is nonsense - when >you have enabled hyperthreading you should use ALL four available virtual >processors. So your measurements are correct. Hint: You DO NOT HAVE 4 >processors, you have only 2 in your machine unfortunately :-) - so you can't play with two Deep >engines against each other - it would be absolutely unclear how much "effective" >CPU-power they would get. Yes, think so! Interesting is to test it under Windows 2003 Server! >Greets, Thomas > >P.S.: I hope that was understandable enough for you Yes, but the result is not "befriedigend ... in German". I will try it tomorrow or next week with an other OS (Windows 2003 Server) and faster Xeon processors! Best Frank
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