On Fri, May 21, 1999 at 01:00:55PM -0600, David G Andersen wrote:
> I looked through the list archives, and couldn't find an answer to this.
>
> Is there a way at either runtime or boot-time (but -Not- compile time) to
> force a multiprocessor Linux system to only recognize one processor, or
> disable SMP entirely? We're trying to get some benchmark numbers, and
> I'd like to avoid pulling a processor out.
>
> (I know, the easy answer is, "keep another non-SMP kernel around", but I'd
> prefer to use the exact same configuration. Ideally, I'd like to not even
> need to reboot, but..).
You can supply the kernel with a boot option (like maxcpus or something like
that, I don't remember), but if you're benchmarking, that's not what you want
to do.
A lot of the spinlock logic and many other things changes dramatically when
you go SMP. An SMP kernel on one CPU will be slower than a non-SMP kernel
on the same CPU, because of the extra logic that just has to go into a SMP
kernel.
You probably want to keep the two kernels around. Use the ``save configuration''
feature to ensure you have two identical setups, then enable/disable SMP on one
of the kernels.
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