Author: Tom Kerrigan
Date: 11:11:24 10/07/03
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On October 06, 2003 at 09:43:55, Robert Hyatt wrote: >On October 06, 2003 at 06:03:21, Tom Kerrigan wrote: > >>On October 04, 2003 at 23:42:01, Robert Hyatt wrote: >> >>>On October 04, 2003 at 21:00:34, Tom Kerrigan wrote: >>> >>>>I had the chance to run my program on a dual P4 Xeon (with hyperthreading). >>>> >>>>First off, there have been some involved arguments about the design and >>>>performance of hyperthreading on this board in the past. I'd like to settle one >>>>argument, namely that single threaded programs do not slow down when >>>>hyperthreading is on. Actually, my program did slow down by 1.3% but I think >>>>this is marginal and easily attributed to the scheduler, not hyperthreading. >>>> >>>>The odd part is that hyperthreading DOES slow down my program when running 2 >>>>threads. With HT off, my program searches 90% more NPS with a 2nd thread. With >>>>HT on, it only searches 53% more NPS. The idle time reported by each thread is >>>>low and the nodes are split evenly, so it seems both processors are slowed down >>>>equally. What must be happening is that HT is activated some (or all?) of the >>>>time while searching but I have no idea what might be activating it. >>> >>> >>>Your explanation is not very clear. You have a dual. Did you run two >>>threads with HT on? Which means that the two threads might run on two >> >>With it on and off. I think I made that pretty clear in my post. > >Yes, but you didn't quite make it clear about how you ran the test. IE I >_think_ you ran two threads on a machine with SMT off, then two threads on >a machine with SMT on. That invites the problem I have discussed here many Right. That's pretty clear to me from: "With HT off, my program searches 90% more NPS with a 2nd thread. With HT on, it only searches 53% more NPS." >times, that no current O/S (except for a windows .net kernel or a linux You keep saying Windows .NET but there is no such thing. I think that's what Windows Server 2003 was going to be called for a while. Do you mean that? Well, in any case, I might as well be using whatever kernel that is. -Tom
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