Author: Vincent Diepeveen
Date: 09:11:59 09/17/03
Go up one level in this thread
On September 17, 2003 at 11:22:58, Robert Hyatt wrote: >On September 16, 2003 at 22:30:47, Vincent Diepeveen wrote: > >>On September 15, 2003 at 14:16:38, Robert Hyatt wrote: >> >>>On September 15, 2003 at 13:18:28, Gian-Carlo Pascutto wrote: >>> >>>>On September 14, 2003 at 12:52:54, Sietel Monic wrote: >>>> >>>>>My friend runs dual proccessors using hyperthreading so gets 4 threads, I know >>>>>this is bad for chess. Just dont know why >>>> >>>>This is ok. Running with 2 threads on a dual processor with hyperthreading >>>>enabled is _not_, unless you're running Linux 2.4.x or Windows Server 2003. >> >>You sure of this bob? > >I am certain. I have duals all over the place, running 2.4.20 and 2.4.21 (I Does that say 2.4.20-NUMA or does it only say 2.4.20 x86 ? But in general i agree. i find the linux OS as a whole a joke at NUMA machines. And kernel 2.6 won't be much better either i bet. >did say I had not tested 2.4.22 yet). Also, your question is in the wrong >place. I didn't write the above. GCP did. I responded to it (the response >appears below).. > > > > >> >>QUADopteron:/diep/latency # uname -a >>Linux QUADopteron 2.4.19-NUMA #3 SMP Wed Jul 2 18:34:37 CDT 2003 x86_64 unknown >> >>Perhaps all you need is a special extension to the kernel. >We are talking about hyper-threading. 4 logical processors with two real >processors. What are you talking about? The opteron is not hyper-threaded. >The issue is that the O/S has to recognize that with only two runnable processes >on a dual-cpu hyper-threaded machine, it needs to run each process on a >different physical processor for max performance, rather than running both on >two logical processors that are on the same physical processor, which would >run much slower. > > >> >>>Linux 2.4.x won't cut it either. I use 2.4.21 and it is _not_ SMT-aware. IE >>>it will certainly recognize 4 processors, but it doesn't realize that if there >>>are just two computational tasks to run, they should be run on two physical >>>processors. 2.4 just runs them on any two logical processors. When the two >>>logical processors are on one physical processor, this performs poorly. Ingo >>>Molnar did a scheduler that addresses this (or maybe Rick did it). And it works >>>well (it has two run queues, one for each physical procesor, rather than four, >>>one for each logical processor.) But that isn't in mainstream 2.4 yet (I have >>>not looked at 2.4.22 closely so it _could_ be there). >>> >>>> >>>>-- >>>>GCP
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