Re: getting processor numbers

["H. Peter Anvin" <hpa@zytor.com>]

Ulrich Drepper wrote:
> Davide Libenzi wrote:
>> It sucks when seen from a micro-bench POV, but does it really matter 
>> overall? The vast majority of software usually calls 
>> sysconf(_SC_NPROCESSORS_*) with very little frequency (mostly once at 
>> initialization time) anyway. That's what 50us / call?
> 
> This is not today's situation.  Yes, 10 years ago when I added the
> support to glibc it wasn't much of a problem.  But times change.  As I
> said before in this thread, OpenMP by default scales the number of
> threads used for a parallel loops depending on the number of available
> processors/cores and therefore the number must be retrieved every time
> (with perhaps minimal caching of a few secs, but this requires
> gettimeofday calls...).  All of a sudden this is not micro benchmark
> anymore.  It's a real issue which we only became aware of because it is
> noticeable in real life.

Sounds like it would need a device which can be waited upon for changes.

	-hpa