Author: Robert Hyatt
Date: 11:45:00 10/05/03
Go up one level in this thread
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...
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