Author: Tom Kerrigan
Date: 00:06:56 04/11/03
Go up one level in this thread
On April 10, 2003 at 23:16:46, Robert Hyatt wrote: >On April 10, 2003 at 20:21:09, Tom Kerrigan wrote: > >>On April 10, 2003 at 17:07:29, Robert Hyatt wrote: >> >>>On April 10, 2003 at 14:51:11, Anthony Cozzie wrote: >>> >>>>>But I don't buy the 50% stuff, the cpu is not that simple internally. One >>>>>thread will run at >>>>>nearly full speed and the other gets slipped into the gaps, which is what I see >>>>>(at least) when >>>>>running Crafty. >>>> >>>>This statement seems counterintuitive to me. If one thread is given a higher >>>>priority in the CPU, than the OS would need to take this into account (and not >>>>just with PAUSE). Could you add a little debugging code to crafty and measure >>>>how many nodes are computed by each thread on a run of your dual xeon? I'm very >>>>curious if it is a 40/40/10/10 split or a 25/25/25/25 split (the latter seems >>>>more logical to me). >>>> >>>>anthony >>> >>> >>>I can't do it, because the threads are not bound to a logical processor, and >>>they bounce around. >> >>Oh, think a little. >> >>Run two instances of single-thread Crafty and search positions with each. Then >>you will see exactly how the processor's time is divided. I'll eat my hat if you >>see 100%-10% instead of 55%-55%. >> >>-Tom > > >Go look up Ingo Molnar's Linux test (he is one of the kernel developers and he >wrote the original specifications for a SMT-aware kernel scheduler). > >His numbers bounced all over creation. 90-10 was as common as 50-50, which was >why he got interested as I was asking questions and nobody had any answers... > >They were hardly _ever_ 50 50. They were usually _way_ off balance. I tried. Do you know how many hundreds of search results you get when you look up Ingo Molnar and hyperthreading on Google? You'll have to give us something a _little_ less worthless than that to go on. And instead of referring to somebody else, why not just run a couple copies of Crafty like I suggested? How long could it possibly take? A couple minutes? -Tom
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