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    SubjectRe: [PATCH -v5][RFC]: mutex: implement adaptive spinning

    On Wed, 7 Jan 2009, Linus Torvalds wrote:
    > >
    > > "Is get_task_struct() really that bad?"
    > Yes. It's an atomic access (two, in fact, since you need to release it
    > too), which is a huge deal if we're talking about a timing-critical
    > section of code.

    There's another issue: you also need to lock the thing that gives you the
    task pointer in the first place. So it's not sufficient to do
    get_task_struct(), you also need to do it within a context where you know
    that the pointer is not going away _while_ you do it.

    And with the mutexes clearing the ->owner field without even holding the
    spinlock, that is not a guarantee we can easily get any way. Maybe we'd
    need to hold the tasklist_lock or something.


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      Last update: 2009-01-08 00:23    [W:0.025 / U:6.252 seconds]
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