[Bug malloc/25817] Tune the number of malloc arenas based on the CPU affinity mask

["fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=25817

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|NEW                         |RESOLVED
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=30945

--- Comment #3 from Florian Weimer <fweimer at redhat dot com> ---
We tried to implement this, but it didn't work and had to reverted:

commit 472894d2cfee5751b44c0aaa71ed87df81c8e62e
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Wed Oct 11 13:43:56 2023 -0300

    malloc: Use __get_nprocs on arena_get2 (BZ 30945)

    This restore the 2.33 semantic for arena_get2.  It was changed by
    11a02b035b46 to avoid arena_get2 call malloc (back when __get_nproc
    was refactored to use an scratch_buffer - 903bc7dcc2acafc).  The
    __get_nproc was refactored over then and now it also avoid to call
    malloc.

    The 11a02b035b46 did not take in consideration any performance
    implication, which should have been discussed properly.  The
    __get_nprocs_sched is still used as a fallback mechanism if procfs
    and sysfs is not acessible.

    Checked on x86_64-linux-gnu.
    Reviewed-by: DJ Delorie <dj@redhat.com>

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