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    SubjectRe: [PATCH] io stalls
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    On Wed, 2003-06-11 at 22:41, Nick Piggin wrote:

    > >I think the only time we really need to wakeup more than one waiter is
    > >when we hit the q->batch_request mark. After that, each new request
    > >that is freed can be matched with a single waiter, and we know that any
    > >previously finished requests have probably already been matched to their
    > >own waiter.
    > >
    > >
    > Nope. Not even then. Each retiring request should submit
    > a wake up, and the process will submit another request.
    > So the number of requests will be held at the batch_request
    > mark until no more waiters.
    >
    > Now that begs the question, why have batch_requests anymore?
    > It no longer does anything.
    >

    We've got many flavors of the patch discussed in this thread, so this
    needs a little qualification. When get_request_wait_wakeup wakes one of
    the waiters (as in the patch I sent yesterday), you want to make sure
    that after you wake the first waiter there is a request available for
    the proccess he is going to wake up, and so on for each other waiter.

    I did a quick test of this yesterday, and under the 20 proc iozone test,
    turning off batch_requests more than doubled the number of context
    switches hit during the run, I'm assuming this was from wakeups that
    failed to find requests.

    I'm doing a few tests with Andrea's new get_request_wait_wakeup ideas
    and wake_up_nr.

    -chris


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