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    SubjectRe: [PATCH] Replace completions with semaphores

    On Sat, 2008-04-12 at 11:26 -0600, Matthew Wilcox wrote:

    > It would look bloody odd to write (code taken from megasas_mgmt_ioctl_fw() in
    > drivers/scsi/megaraid/megaraid_sas.c):
    > if (wait_for_completion_interruptible(&instance->ioctl_completion)) {
    > error = -ERESTARTSYS;
    > goto out_kfree_ioc;
    > }
    > error = megasas_mgmt_fw_ioctl(instance, user_ioc, ioc);
    > complete(&instance->ioctl_sem);
    > What I'm trying to get a feeling for is whether people find it similarly
    > odd to use semaphores where we currently use completions. We *used*
    > to, but I don't find that a compelling reason.

    The above doesn't look all that odd to me. It may be that you've seen
    semaphores in that position in the past and just expect to see them.

    > Arnd contacted me off-list and made the very sensible suggestion of:
    > struct completion {
    > struct semaphore sem;
    > }
    > That lets us eliminate the duplicate code since all the completion
    > functions become very thin wrappers around semaphore operations.
    > I'll note that the semaphore code I hae queued for 2.6.26 is slightly
    > more efficient than the current implementation of completions because
    > completions use the generic waitqueue code and thus do an indirect
    > function call per wakeup. Of course, there's no reason completions
    > couldn't use the same technique as my semaphore code ... but then they
    > would be identical to semaphores ;-)

    I would just re-write completions keeping the name and API in tact, make
    them better and just leave semaphores alone..


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