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    SubjectRe: [PATCH] cfq-prio #2


    Jens Axboe wrote:

    >On Tue, Nov 11 2003, Nick Piggin wrote:
    >
    >>
    >>Jens Axboe wrote:
    >>
    >>
    >>>Hi,
    >>>
    >>>
    >>>
    >>Hi Jens
    >>
    >>
    >>>@@ -1553,6 +1559,10 @@
    >>> struct io_context *ioc = get_io_context(gfp_mask);
    >>>
    >>> spin_lock_irq(q->queue_lock);
    >>>+
    >>>+ if (!elv_may_queue(q, rw))
    >>>+ goto out_lock;
    >>>+
    >>> if (rl->count[rw]+1 >= q->nr_requests) {
    >>> /*
    >>> * The queue will fill after this allocation, so set it as
    >>>@@ -1566,15 +1576,12 @@
    >>> }
    >>> }
    >>>
    >>>- if (blk_queue_full(q, rw)
    >>>- && !ioc_batching(ioc) && !elv_may_queue(q, rw)) {
    >>>
    >>>
    >>I know I hijacked elv_may_queue from you... any chance we could seperate
    >>these so our schedulers can live in peace? ;)
    >>
    >
    >IOW, you completely broke it! I'm just changing it back to the
    >original. When was this done, btw? Just discovered it when updating the
    >patch. Pretty annoying...
    >

    You acked the change actually :P
    I guess it was done in mainline when AS was merged.

    >
    >>Maybe my version should be called elv_force_queue?
    >>
    >
    >I just hate to see more of these, really. The original idea for
    >may_queue was just that, may this process queue io or not. We can make
    >it return something else, though, to indicate whether the process must
    >be able to queue. Is it really needed?
    >

    Its quite important. If the queue is full, and AS is waiting for a process
    to submit a request, its got a long wait.

    Maybe a lower limit for per process nr_requests. Ie. you may queue if this
    queue has less than 128 requests _or_ you have less than 8 requests
    outstanding. This would solve my problem. It would also give you a much more
    appropriate scaling for server workloads, I think. Still, thats quite a
    change in behaviour (simple to code though).


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