On Tue, 7 Sep 1999, John F. Nixon wrote:
> Robert M. Hyatt writes:
>
> > > Modern CPUs can have many instructions executing in parallel. In
> > > particular, the Alpha 21264 can have up to 4 integer instructions
> > > executing per CPU cycle, and two floating point instructions per
> > > cycle. It is possible for different threads to have instructions in
> > > process at the same time on the same CPU.
> >
> > No it isn't. Superscalar processors execute multiple instructions in
> > one cycle... but they have exactly _one_ program counter. So there is
> > _no_ way for two threads to issue instructions to the same cpu at the same
> > time.
>
> You are misreading my claim. I'm not saying threads can issue
> instructions simultaneously. I'm saying the processor can have a
> mixture of instructions from different threads in execution at once.
Maybe what we have here is a failure to communicate. :)
But in any case, how would you issue instructions from different threads
to a single CPU/FPU combination? Unless you hand-code the two threads
into a single program thread, but then they really aren't two threads
any longer...
Maybe just semantics?
Bob
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