Re: Process scheduling in multiprocessor systems
On Tue, 6 Feb 2007 18:18:53 -0500, "Prasanna Padmanabhan"
<prasannap@citrixnospamtolerated.com> wrote:
I am trying to understand something.
I am running the following program, a maximally tight loop, on a Windows
2003 server, that is running on a dual Processor machine (Intel Xeon).
main()
{
__asm
{
again:jmp again;
}
}
I notice that the CPU usage suddenely spikes up, on both processors to about
50% (each).
Only when I run another instance of the same program, the CPU usage is a
100% on both processors.
Why didn't the first's processor's uage spike upto 100% when running only 1
instance of the above program?
Is the same process running on 2 different processors AT THE SAME TIME and
they are each spending half their time
in running this infinite loop?
Thanks,
Prasanna
It's certainly not running concurrently on the two CPUs. I believe Windows
is merely bouncing it back and forth between the two. Presumably Windows
knows what it's doing, and I'm not sure what the larger picture is here,
but if you explicitly set the processor affinity, you should be able to
confine it to one or the other. On my Core 2 Duo system, WinXP does about
an 80/20 split, rather than the 50/50 you're observing. You might want to
ask about this in microsoft.public.win32.programmer.kernel. Potentially
useful books that come to mind include those by Richter and
Russinovich/Solomon. (The book names change, but the authors don't, and I
can remember the authors better than the titles.)
--
Doug Harrison
Visual C++ MVP