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    SubjectRe: Device or HBA level QD throttling creates randomness in sequetial workload
    Date
    On Mon, 2017-01-30 at 19:22 +0530, Kashyap Desai wrote:
    > - if (atomic_inc_return(&instance->fw_outstanding) >
    > - instance->host->can_queue) {
    > - atomic_dec(&instance->fw_outstanding);
    > - return SCSI_MLQUEUE_HOST_BUSY;
    > - }
    > + if (atomic_inc_return(&instance->fw_outstanding) > safe_can_queue) {
    > + is_nonrot = blk_queue_nonrot(scmd->device->request_queue);
    > + /* For rotational device wait for sometime to get fusion command
    > from pool.
    > + * This is just to reduce proactive re-queue at mid layer which is
    > not
    > + * sending sorted IO in SCSI.MQ mode.
    > + */
    > + if (!is_nonrot)
    > + udelay(100);
    > + }

    The SCSI core does not allow to sleep inside the queuecommand() callback
    function.

    Bart.
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