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    SubjectRe: [tip:core/locking 1/3] lockdep:reintroduce generation count to make BFS faster
    From
    2009/7/22 Peter Zijlstra <a.p.zijlstra@chello.nl>:
    > On Wed, 2009-07-22 at 20:58 +0800, tom.leiming@gmail.com wrote:
    >> From: Ming Lei <tom.leiming@gmail.com>
    >>
    >> We still can apply DaveM's generation count optimization to
    >> BFS, so reintroduce it.
    >
    > Please elaborate, changelogs are important.

    Sorry, I'll resend the patches and provide a elaborate changlogs.


    >
    > You fail to explain why it still applies and what the gains are.
    >
    > (I can guess, but you explaining makes sure we're on the same page)
    >

    gains:
    1), avoid to allocate the bfs_accessed array;

    2), remove the
    bitmap_zero(bfs_accessed, MAX_LOCKDEP_ENTRIES);
    in each BFS, which is a little time consuming since
    MAX_LOCKDEP_ENTRIES
    is very large.(16384UL)

    --
    Lei Ming


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