Author: Vincent Diepeveen
Date: 10:44:15 10/05/03
Go up one level in this thread
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.
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