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    SubjectRe: RT and XFS
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    On Thu, 2005-07-14 at 13:50 +1000, Dave Chinner wrote:
    > Now that I've read the thread, I see it's not mrlocks that is the
    > issue with unlocking in a different context - it's semaphores.
    >
    > All the pagebuf synchronisation is done with a semaphore because
    > it's held across the I/O and it's _most definitely_ released in a
    > different context when doing async I/O. Just about all metadata I/O
    > is async because once the transaction has been logged to disk we
    > don't need to write these buffers out synchronously. Not to mention
    > the log I/O completion unlocks the buffers in a transaction in a
    > different context as well.
    >
    > The whole point of using a semaphore in the pagebuf is because there
    > is no tracking of who "owns" the lock so we can actually release it
    > in a different context. Semaphores were invented for this purpose,
    > and we use them in the way they were intended. ;)

    Where is the that semaphore spec, is that posix ? There is a new
    construct called "complete" that is good for this type of stuff too. No
    owner needed , just something running, and something waiting till it
    completes.

    > Realistically, I seriously doubt the need for any sort of rt changes
    > to these semaphores. They can be held for indeterminant periods of
    > time potentially across multiple disk I/Os (e.g. when held locked in
    > a transaction that requires more metadata to be read in from disk to
    > make progress). Hence there is no really no point in making them RT
    > aware because if you end up waiting on one of them you can forget
    > about pretty much any RT guarantee that you've ever given....

    PI is always good, cause it allows the tracking of what is high
    priority , and what is not .

    Daniel

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