Author: Tom Kerrigan
Date: 03:07:09 10/06/03
Go up one level in this thread
On October 05, 2003 at 14:56:38, Vincent Diepeveen wrote: >On October 05, 2003 at 14:45:00, Robert Hyatt wrote: > >>On October 05, 2003 at 13:44:15, Vincent Diepeveen wrote: >> >>>On October 04, 2003 at 23:44:03, Robert Hyatt wrote: >>> >>>>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. >>> >>>Not really, all reports i saw here from non-Hyatt and non-Nalimov machines >>>report for the same versions 10-15% for crafty. >> >>And 10%-15% is _drastically_ different than 20%, right? >> >>learn some math. >> >>this varies significantly, on the same machine... > >You tested just 6 postions, so that renders your results pretty useless. > >The others had tested around 30 positions. > >So even if we still take the average it's closer to 10% than it is to 30%. > >Nalimov just said 30% without much of a proof. You sound all indignant, like Bob & Eugene are lying, but at the same time it seems clear to you that different tests yield different results. You can think the tests they ran were not representative but it's stupid to be upset over the actual #s they got. -Tom
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