Author: Robert Hyatt
Date: 21:54:39 08/24/02
Go up one level in this thread
On August 23, 2002 at 12:33:43, Yen Art Tham wrote: >On August 22, 2002 at 17:13:47, Robert Hyatt wrote: > >>On August 22, 2002 at 16:25:10, Yen Art Tham wrote: >> >>>On August 22, 2002 at 13:43:06, Robert Hyatt wrote: >>> >>>>On August 22, 2002 at 13:38:17, Rajen Gupta wrote: >>>> >>>>>in practical terms how much faster would an 8 way processor be for the most >>>>>scaleable commercial chess programme which i believe is shredder? >>>>> >>>>>rajen >>>> >>>> >>>>If it turned out to be 1.5X faster than a 4-way that would probably be >>>>a huge plus... memory is a problem on 2-way and 8 way boxes... >>> >>> >>>In what way is memory a "problem" on a dual? >>>Please elaborate. >>> >>>yat >> >> >>Memory bandwidth is severely limited on a normal PC. On a dual, you >>simply add a second processor, which then competes for memory bandwidth >>with the first processor. As a result, a dual machine is generally not >>2x faster than a single. >> >>For the quad (4 cpu machines) the manufacturers use a more sophisticated >>chipset that provides 4x the memory bandwidth by doing 4-way memory >>interleaving. As a result, on a quad, each CPU sees about the same >>bandwidth potential as a single-cpu machine sees. >> >>On an 8-way box, the chipset still relies on 4-way interleaving, but you >>have 8 processors. IE it will perform about like 4 dual-cpu machines, >>which is not quite as good as you would expect from 8 cpus... > > >Would the problem be solved with the Opteron which has integrated >memory controller? 2 cpu, 2 memory controller. But one memory bus. That is the problem. Both controllers can't read from a single "bank" of memory at the same time. That is how interleaving cheats the issue. It reads 4 64 bit values at once from 4 "banks". But you have to have a memory system that supports that with banks... I know nothing about the opteron yet...
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