The article says at another place that the "overall of the execution units"
in the P-IV
are UNUSED for 75% of the time. And that is the base idea behind HT.

Exampel:
"Pipeline stall" when doing unpredicted branches, Integer units unused while
there is FP-OP in Progress etc.

So I would say two things:

1. the speed increase can be 25% to max. of 75%  IF the code is specially
done for a hyperthreaded system,
    done to "keep all execution units busy". Exactly that: Keep ALL units
busy. Means: intermix FP & ALU
    code IN diffrent threads.

2. Normal "multithreaded code can even slow down the program execution
significantly by blocking the threads from memory/by clearing cache lines
(up to -25% !)..

3. It would be better to have a "real" SMP-Core with two physical processors
so you could really get a speed improvement when usinf two FPU-intensive
threads.

4. Btw. that was my conclusion from the iX article. It couldn't verify it.
So lets wait with the last conclusion till we see the first real "nothwood
HT"-Processors. Should be soon the case ....

--Theo

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