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    Subjectbug in elevator/cfq regarding start_time?
    Hi Jens,
    I found that the start_time is not monotonic in the cfqq fifo_list.
    The problem seems to be that:
    * attempt_merge overrides one of the start_time:
    if (time_after(req->start_time, next->start_time))
    req->start_time = next->start_time;
    * then it calls elv_merge_requests, that in turn invokes cfq's
    elevator_merge_req_fn, i.e. cfq_merged_requests
    * cfq_merged_requests checks start_times to decide whether requests
    need to be repositioned
    if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
    time_before(next->start_time, rq->start_time))
    list_move(&rq->queuelist, &next->queuelist);

    Other I/O schedulers are not affected, since none of them uses
    start_time explicitly, but they have a copy in one of the private



    dott. Corrado Zoccolo
    PhD - Department of Computer Science - University of Pisa, Italy

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      Last update: 2009-10-04 22:57    [W:0.019 / U:72.736 seconds]
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