Author: Robert Hyatt
Date: 20:00:58 04/09/03
Go up one level in this thread
On April 09, 2003 at 21:46:19, Anthony Cozzie wrote: >Crafty seems to be unique in that it gets a lot from hyperthreading - Fritz does >not, as Charles' benchmarks show. > >SMT is not a guaranteed win. For SMT to accelerate a chess program, the >following inequality must be true: > >(1+S)*1.7/2 > 1 > >=> S >= 17% (approximately: SMP speedup varies a lot over various positions) > >In other words, Crafty on a PIV will get 30% from hyperthreading and a positive >speedup, Fritz on a PIV will get 10% from hyperthreading and a relative slowdown >in search (even as NPS go down). > >anthony I do _not_ follow a discussion which talks about a slowdown. If a program produces _any_ speedup on two cpus, then it should produce a speedup using less than two cpus, but more than one cpu (SMT in other words). If your NPS goes up by 10%, then with a 1.7x multiplier on two real cpus, the program should run 1.07X faster using SMT. If the NPS goes _down_ with SMT on, something else is broken, either in the software or the hardware.
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