Author: Vincent Diepeveen
Date: 11:56:38 10/05/03
Go up one level in this thread
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. Best regards, Vincent
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