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Technology Stocks : Advanced Micro Devices - Moderated (AMD)
AMD 192.49-4.0%Feb 5 3:59 PM EST
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To: fyodor_ who wrote (53495)8/31/2001 8:49:07 PM
From: Saturn VRead Replies (1) of 275872
 
Ref < adding HyperThreading doesn't increase the resources of a processor. It only allows the processor to use these resources better. If programs are already written in such a way that the processor resources are the bottle-neck, no increase in performance will be observed >

Today it is impossible for the processor ALU and FP resources to be the the bottleneck. I am familiar with code optimisation at the assembler level, and today the multiple ALU and FP sit unutilized most of the time. Even the double speed ALU of the P4 is overkill.

The most frequent bottleneck is the the memory. The biggest killer is a L2 miss, which can stall the ALU for a 100 cycles or more.A L1 miss will cause a stall of several cycles too. However if the system is hyperthreaded, if one thread is stalled the other thread is free to use the ALUs and The FPU.

Similarly FPU operation can take a few cycles on one thread. The ALUs will sit idle for a single thread processor because of dependencies of subsequent operations on the result. However the second thread can use the ALUs.

Obviously the thruput will not be 2X of a single theaded system. But an improved thruput of 15%-40% sounds plausible.
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