Author: Robert Hyatt
Date: 20:44:03 10/04/03
Go up one level in this thread
On October 04, 2003 at 21:09:23, Vincent Diepeveen 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). > >which OS and what version number of the os and what release number? > >pretty crucial. > >>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. >> >>Also odd is that HT seems to be decreasing the efficiency of the search. With HT >>off, my program's time-to-ply is 64% faster with 2 threads but with HT on, it's >>only 21% faster. The time-to-ply:NPS ratios are 0.86 and 0.79 respectively. >> >>Running 4 threads with HT on results in a 15% NPS/6% time-to-ply speedup over 2 >>threads. >> >>In other words, there's no contest between running 2 threads (HT off) vs. >>running 4 threads (HT on). The former wins hands down for my program. >> >>-Tom > >Your thing is searching parallel nowadays and we do talk about a chessprogram >here? > >Doesn't take away that it is not easy to profit from HT. > >Basically HT only works well at intel test machines it seems. > >those do HT a lot better than non-test machines. > >it is confirmed again in www.aceshardware.com > >25% speedup (in nodes a second) for diep is just too much (single P4 EE 3.4Ghz) >i bet production machines that we can buy in the shops soon won't show at single >cpu P4 EE 3.4Ghz a speedup of 25% like aceshardware.com has tested. Anyway i >kept the executable to proof my guess there in the future when the p4 ee is >released or when i can run at a P4 3.2Ghz C (also showed 25% speedup in nps >thanks to HT for current diep version). > >best regards, >vincent Several have run this test with Crafty. SMT on is 20-30% faster in NPS for my program, on my dual 2.8, which is not a "test machine". Eugene posted similar numbers for a dual he has. Others have also reproduced this with no problems.
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