Re: a dozen cpu's on a chip

On May 9, 7:27 pm, krw <k...@xxxxxxxxxxxxxxxx> wrote:
In article <3n6624pu6762nup9apu3crj5vh1uu6f...@xxxxxxx>,
[....]
Right. Amybe a few cpu's would have serious floating point power, or a
few separate fp engines could be assigned to cpu's as needed. Lots of
cpu's, doing stuff like file i/o or serial stuff, could be less
powerful. I suppose we'll always need special graphics hardware, but
just a few of those per chip.

Asymmetric multiprocessing makes the scheduler's life more
complicated. Since the scheduler is part of the OS, and the OS is
most often M$, this isn't a good idea, IMO. ;-) Hardware is cheap
(so cheap PowerPC is including decimal FPUs). Throw the FPU on
every node, whether its needed or not.

You are suggesting a hardware fix for a problem that doesn't need to
exist. Since a very high performance machine by definition is not
running anything M$, there is no need to build in hardware corrections
for the errors in their products.

Since the FPU contains a great many transistors and those transistors
could be use to make another CPU, it would make sense to not put in
the FPU in favor of another full CPU.


It also would make sense to do things like memory moves in the "Memory
Mismanagement Unit" since the values don't need to be modified on the
way through.

This will make it a lot harder to say how many CPUs are in a chip. If
there is only as much hardware as 200 full CPUs but 500 threads can be
running at the same time, do you call it 200 or 500 CPUs.

Next step is to get rid of task swapping and threads altogether. One
CPU is the OS, and one cpu gets assigned per process.

Which negates what you say above. Running a task, then getting an
exception because you don't have an instruction you thought you had
is expensive.

But if you know which tasks never do floating operations, you can
leave them on the CPU without an FPU. If you don't know you only need
to perform the experiment once and suffer the overhead of moving the
task to a different CPU once.


--
Keith

.

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