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    SubjectRe: Delayed interrupt work, thread pools
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    On Tue, 2008-07-01 at 20:39 -0500, Dean Nelson wrote:
    > As Robin, mentioned XPC manages a pool of kthreads that can (for performance
    > reasons) be quickly awakened by an interrupt handler and that are able to
    > block for indefinite periods of time.
    >
    > In drivers/misc/sgi-xp/xpc_main.c you'll find a rather simplistic attempt
    > at maintaining this pool of kthreads.
    >
    > The kthreads are activated by calling xpc_activate_kthreads(). Either idle
    > kthreads are awakened or new kthreads are created if a sufficent number of
    > idle kthreads are not available.
    >
    > Once finished with current 'work' a kthread waits for new work by calling
    > wait_event_interruptible_exclusive(). (The call is found in
    > xpc_kthread_waitmsgs().)
    >
    > The number of idle kthreads is limited as is the total number of kthreads
    > allowed to exist concurrently.
    >
    > It's certainly not optimal in the way it maintains the number of kthreads
    > in the pool over time, but I've not had the time to spare to make it better.
    >
    > I'd love it if a general mechanism were provided so that XPC could get out
    > of maintaining its own pool.

    Thanks. That makes one existing in-tree user and a one likely WIP user,
    probably enough to move forward :-)

    I'll look at your implementation and discuss internally see what our
    specific needs in term of number of threads etc... look like.

    I might come up with something simple first (ie, generalizing your
    current implementation for example) and then look at some smarter
    management of the thread pools.

    Cheers,
    Ben.




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