[glibc] Fix Linux sysconf(_SC_NPROCESSORS_[CONF|ONLN]) performance problem

[Klaus Dittrich]

Am 06/16/11 20:25, schrieb Linus Torvalds:
> On Thu, Jun 16, 2011 at 1:04 PM, Paul Eggert<eggert@cs.ucla.edu>  wrote:
>>
>> "Stale" could mean "the tv_sec value doesn't match", or it could be something
>> fancier; I doubt whether it matters much.
>
> I certainly think that would be a lot better than what glibc does now
> - at least limiting the /proc/stat reading to a maximum of once per
> second or similar.
>
> And it could be combined with the patch I just sent out (which ends up
> parsing /sys/devices/system/cpu/online every time. It's a cheaper (and
> more obvious) file than /proc/stat, but it's still not zero-cost.
>
>                         Linus

As, at least today, most users run with a constant number of cpus,
how about a configure option like num_of_cpus_may_vary in either kernel 
or glibc.

This would give the time to discuss calmly a better solution for the others.

-- 
Klaus