Author: Robert Hyatt
Date: 18:45:19 03/24/02
Go up one level in this thread
On March 24, 2002 at 17:13:53, Tom Kerrigan wrote: >On March 24, 2002 at 00:02:50, Robert Hyatt wrote: > >>On March 23, 2002 at 16:09:55, Tom Kerrigan wrote: >> >>>On March 23, 2002 at 13:38:45, Dan Andersson wrote: >>> >>>>SMT is of little or no consequence to chess programs. It might even slow it >>>>down. You don't think it automatically doubles the amount of functional units on >>>>a given CPU, do you? >>> >>>You're completely missing the point. SMT was invented and implemented because >>>most of a chip's functional units are idle at any given point in time--using >>>them for another thread gives you free performance. >>> >>>I haven't seen any benchmarks yet, but a quad P4 Xeon will appear to software as >>>an 8-way system and while it will probably not be as fast as a full-on 8-way >>>system, it will be much faster than a 4-thread system. >>> >>>-Tom >> >>This is only true of _one_ of the two threads can run mainly out of cache. >>The processor will have the other thread stalled waiting on memory reads or >>writes. If the second thread needs memory, it is over... But if it can run >>out of cache, it can fill in the gaps nicely... > >Do you have a reference for the P4 only switching threads on main memory >accesses? > >-Tom That was the explanation the Intel engineers used when they first announced this. They made the comparison to processes and I/O on a conventional CPU, and took the analogy to nano-scale with threads within a CPU and memory blocks. I don't know if they do anything _else_ personally, as I haven't particularly been that interested since it isn't being used much yet...
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