Re: a dozen cpu's on a chip

On Fri, 9 May 2008 22:27:56 -0400, krw <krw@xxxxxxxxxxxxxxxx> wrote:

In article <3n6624pu6762nup9apu3crj5vh1uu6fqbn@xxxxxxx>,
jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx says...
On Thu, 8 May 2008 07:42:04 -0700 (PDT), MooseFET <kensmith@xxxxxxxxx>
wrote:

On May 7, 7:48 pm, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
http://www.eetimes.com/news/latest/showArticle.jhtml;jsessionid=CESEX...

I bet we'll see 256 one of these days.

When you get to large numbers of CPUs it seems to make sense to stop
making them identical. For servers this would be doubly so. Many of
the CPUs won't need to do floating point operations.

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.

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.

Why would you get an exception? If a device driver doesn't need fp
opcodes, run it on one of the many cpu's that doesn't have floating
point. And vice versa. <> rocket science.

John

.

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