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    SubjectRe: [PATCH -v9][RFC] mutex: implement adaptive spinning

    * Peter Zijlstra <peterz@infradead.org> wrote:

    > > Now you're forcing the slow-path on unlock. Maybe it was intentional,
    > > maybe it wasn't. Did you perhaps mean
    > >
    > > if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
    > >
    > > here? I thought we agreed it was safe, if only because it should be
    > > equivalent to just having done "mutex_trylock()" instead of a "real"
    > > lock sequence.
    >
    > Yes, that was an 'accident' from -v8, yes we did think the cmpxchg was
    > good, however I did get some spurious lockups on -v7, and I only noticed
    > the thing after I'd done most of the testing, so I decided to let it be
    > for now.
    >
    > Let me put the cmpxchg back in and see if this is all still good (only
    > 3*2*2 configs to test :-).

    i saw sporadic lockups with -v7 too, so if you send a -v10 with Linus's
    sequence for the unlock it takes about an hour of testing to check whether
    it still occurs.

    Ingo


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