Re: [musl] [BUG] sysconf implementing _SC_NPROCESSORS_(CONF|ONLN) incorrectly

[Florian Weimer <fw@deneb.enyo.de>]

* Norbert Lange:

> How should  one deal with this?
> I understand that the semantics are vague, but given that musl now
> implements this
> function, it will make detection and fallback hard (especially as musl
> doesn't wants to be identified by the likes of macros).
>
> As it is now, just using the affinity mask definitely cant be useful,
> an application wanting that behavior should be patched to
> use that function directly.
> If musl would not define the _SC_NPROCESSORS_* macros (but still keep
> the implementation),
> this could be used for compile-time detection atleast. Enabling the
> current implementation would be
> just a matter of explicitly defining those macros.

_SC_NPROCESSORS_* as implemented in glibc is bad because those values
are not adjusted by cgroups, so it can grossly overestimate available
resources.

The cgroups interfaces themselves are not stable and very complicated.
I don't think it's a good idea to target them, especially not from
code that is expected to be linked statically into applications.

Given that, I'm not sure that glibc's way is a significant
improvement.  musl should perhaps be changed to cope more gracefully
with a sched_getaffinity failure, though (by not reporting a UP
environment by accident).