Author: Robert Hyatt
Date: 06:48:40 10/06/03
Go up one level in this thread
On October 06, 2003 at 06:07:09, Tom Kerrigan wrote: >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 The only numbers that matter are the numbers _Vincent_ produces. All other numbers are "rude" or "wrong" or "impossible" etc. Surely you have recognized that, even when he is the _only_ person that reports such numbers (one example: Crafty on a dual produces _no_ speedup. yet everybody that has tested has shown an average speedup of around 1.7, except for my dual xeon which is not producing 2x NPS on a dual, when it produces 2X with 2 processors and 4X with 4 processors on my quad boxes.) Arguing with his "proofs" is hopeless...
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