Because two hyperthreads some of the same hardware. And some of that hardware is required to do the spinning. Just a thought.
Found this with a quick search: http://archives.postgresql.org/pgsql-patches/2003-12/msg00345.php On Sat, Aug 11, 2012 at 8:45 PM, Hideki Kato <hideki_ka...@ybb.ne.jp> wrote: > Michael Williams: > <CAB0EdYWgs=gjsnt9rmkj8-utlg72nyxnafvd-8iq_pjjf_j...@mail.gmail.com>: >>I wonder if spin-lock hurts hyperthreading. > > Why do you think so? If a spin-lock accesses memory and waits, > simply another thread runs. That's all. > > Hideki > >>On Sat, Aug 11, 2012 at 7:22 PM, Hideki Kato <hideki_ka...@ybb.ne.jp> wrote: >>> Petr Baudis: <20120811145900.gv19...@machine.or.cz>: >>>>On Sat, Aug 11, 2012 at 12:52:12AM -0700, David Fotland wrote: >>>>> Yes, root parallelization with some sharing. >>>>> http://www.personeel.unimaas.nl/G-Chaslot/papers/parallelMCTS.pdf said it >>>>> was good and I tried it and it works well. >>>> >>>>The paper is not so relevant now, since the standard method of most >>>>programs is lockless tree parallelization, which is not covered. >>>>The locking overhead is quite significant, I'd expect, as locking >>>>instructions can AFAIK take hundreds of cycles. >>> >>> With spin-lock or hardware test-and-set instructions, locking overhead >>> is very small. >>> >>>>That said, root parallelization overperforming sequential simulations >>>>is something I never managed to reproduce and that seems rather >>>>surprising to me. It might have something to do with the way priors >>>>are done in the tree or some other engine-specific factors. >>> >>> I believe IBM Power processor's architecture may caused the super-linear >>> acceralaton. >>> >>> Hideki >>> -- >>> Hideki Kato <mailto:hideki_ka...@ybb.ne.jp> >>> _______________________________________________ >>> Computer-go mailing list >>> Computer-go@dvandva.org >>> http://dvandva.org/cgi-bin/mailman/listinfo/computer-go >>_______________________________________________ >>Computer-go mailing list >>Computer-go@dvandva.org >>http://dvandva.org/cgi-bin/mailman/listinfo/computer-go > -- > Hideki Kato <mailto:hideki_ka...@ybb.ne.jp> > _______________________________________________ > Computer-go mailing list > Computer-go@dvandva.org > http://dvandva.org/cgi-bin/mailman/listinfo/computer-go _______________________________________________ Computer-go mailing list Computer-go@dvandva.org http://dvandva.org/cgi-bin/mailman/listinfo/computer-go
