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    SubjectRe: [PATCH 7/9] lib/cpumask: add num_{possible,present,active}_cpus_{eq,gt,le}
    On Sun, Nov 28, 2021 at 05:56:51AM +0100, Michał Mirosław wrote:
    > On Sat, Nov 27, 2021 at 07:57:02PM -0800, Yury Norov wrote:
    > > Add num_{possible,present,active}_cpus_{eq,gt,le} and replace num_*_cpus()
    > > with one of new functions where appropriate. This allows num_*_cpus_*()
    > > to return earlier depending on the condition.
    > [...]
    > > @@ -3193,7 +3193,7 @@ int __init pcpu_page_first_chunk(size_t reserved_size,
    > >
    > > /* allocate pages */
    > > j = 0;
    > > - for (unit = 0; unit < num_possible_cpus(); unit++) {
    > > + for (unit = 0; num_possible_cpus_gt(unit); unit++) {
    >
    > This looks dubious. The old version I could hope the compiler would call
    > num_possible_cpus() only once if it's marked const or pure, but the
    > alternative is going to count the bits every time making this a guaranteed
    > O(n^2) even though the bitmap doesn't change.

    Hmm. This code already unnecessarily calls num_possible_cpus() multiple
    times. Since it doesn't change after early init I would suggest just
    calling it once here.

    Best Regards
    Michał Mirosław

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