[Bug libc/30135] sysconf: _SC_NPROCESSORS*: tweak?

["adhemerval.zanella at linaro dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30135

--- Comment #3 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
(In reply to Steffen Nurpmeso from comment #2)
> . sysconf and _SC_NPROCESSORS_ONLN is the only standardized variant,
> sched_getaffinity() is not a portable interface.
> 
> . I feel "currently available to run threads" pretty much matches that
> CPU_COUNT() thing that nproc(1) uses.
> 
> . For example, look at zstd(1), they use sysconf(_SC_NPROCESSORS_ONLN) to
> realize -T0.  Same for xz(1).
> This is _all_ wrong in my cgroup restricted environment, they potentially
> "over-thread".
> 
> . Quite the opposite, top(1) is to be changed (a bit strange as my version
> is from https://gitlab.com/procps-ng aka /proc based)
> If i run it in a cgroup-mutilated environment with three CPUs, it lists a
> fourth one that is out of scope!
> 
> . I have not checked virtual machines.  It astounds me they use synthesized
> CPU counts instead of the CPU count that truly is available.

Fell free to rehash this discussion on libc-alpha, but as I said we already
tried it and since it turned out to generate a lot of unseen problems we
decided to revert and use sysfs instead.

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