On Mon, 27 Sep 2010, Sean Bruno wrote:
wouldn't it be better to do a sysctlbyname() and use the real value for the
system?
libmemstat contains some useful sample code showing how this might be done.
That was my initial thought (as prodded by scottl and peter).
If it is made dynamic, could this be opening a race condition where the call
to sysctlbyname() returns a count of CPUS that is in turn changed by the
offlining of a CPU? Or am I thinking to much about this?
Yes, you are. MAXCPU is a compile-time constant for kernel builds, so (at
least a the world is today), that can't happen.
I think there's a reasonable argument that MEMSTAT_MAXCPU should be phased out
and all internal structures in libmemstat should be dynamically sized.
However, core counts aren't growing that fast, and it's quite a bit of work,
and probably not worth it just yet.
I'm somewhat averse to using MAXCPU in libmemstat, however, because MAXCPU is
actually not a constant in the general case: FreeBSD/i386, for example,
regularly uses two different values: 1 for !SMP kernels, and 32 for SMP
kernels. That's why libmemstat encodes its own value, for better or worse.
A reasonable alternative would be to replace 32 with MAXCPU * 2, or if we're
feeling particularly optimistic, MAXCPU * 4. Or just another big number, like
256.
Robert
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