Author: Gian-Carlo Pascutto
Date: 00:29:09 11/03/02
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On November 03, 2002 at 02:00:41, Anthony Cozzie wrote: >If I understand SMT correctly, its even more than that. A modern processor has >a lot of functional units lying around. An Athlon can in theory execute 3 >branches, 3 integer instructions, and 3 floating point instructions every >cycle. In reality, most of the time those units are just sitting around. One >of the ideas behind SMT is that you can run 2 threads, and split the >functional units between them. The problem with this (and the reason I was surprised SMT works) is that it only has 3 decoders and a single cache that is used by both processes. It is somewhat irrelevant that you have 9 function units if your processor is decoder-limited (true for most modern cpus). I guess all improvement from SMT is because of memory waiting as Robert describes. -- GCP
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