Author: Robert Hyatt
Date: 20:16:46 04/10/03
Go up one level in this thread
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.
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