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    SubjectRe: [Ksummit-2008-discuss] Delayed interrupt work, thread pools
    On Wed, 2 Jul 2008, Benjamin Herrenschmidt wrote:
    > 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.

    Do the pdflush daemons (from mm/pdflush.c) provide another example?

    Hugh


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