lkml.org 
[lkml]   [2023]   [Mar]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 5/5] cpumask: fix comment of cpumask_xxx
    On Mon, Mar 6, 2023 at 8:07 AM Vernon Yang <vernon2gm@gmail.com> wrote:
    >
    > After commit 596ff4a09b89 ("cpumask: re-introduce constant-sized cpumask
    > optimizations"), the cpumask size is divided into three different case,
    > so fix comment of cpumask_xxx correctly.

    No no.

    Those three cases are meant to be entirely internal optimizations.
    They are literally just "preferred sizes".

    The correct thing to do is always that

    * Returns >= nr_cpu_ids if no cpus set.

    because nr_cpu_ids is always the *smallest* of the access sizes.

    That's exactly why it's a ">=". The CPU mask stuff has always
    historically potentially used a different size than the actual
    nr_cpu_ids, in that it could do word-sized scans even when the machine
    might only have a smaller set of CPUs.

    So the whole "small" vs "large" should be seen entirely internal to
    cpumask.h. We should not expose it outside (sadly, that already
    happened with "nr_cpumask_size", which also was that kind of thing.

    So no, this patch is wrong. If anything, the comments should be strengthened.

    Of course, right now Guenter seems to be reporting a problem with that
    optimization, so unless I figure out what is going on I'll just need
    to revert it anyway.

    Linus

    Linus

    \
     
     \ /
      Last update: 2023-03-27 00:46    [W:7.886 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site