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

[Linus Torvalds]

On Thu, Jun 16, 2011 at 10:58 AM, Samuel Thibault
<samuel.thibault@ens-lyon.org> wrote:
> Linus Torvalds, le Thu 16 Jun 2011 09:38:55 -0700, a écrit :
>>  - cache the value in a static variable, so that if/when there are
>> multiple calls, we don't spend time recalculating the number of CPU's
>> in the system unnecessarily.
>
> Mmm, but what if the process starts with only one allowed CPU, and
> then is given more CPUs? (either by making CPUs online, or by using
> sched_setaffinity from an administration tool).

So remove the use of sched_getaffinity() if you want to.

But the caching is needed, because whatever the process wants, I
guarantee that it doesn't want "slow and crappy".

                           Linus