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    SubjectRe: Problem with aacraid driver in 2.5.63-bk-latest
    Alan Cox wrote:
    > On Wed, 2003-03-12 at 23:06, Mark Haverkamp wrote:
    >>During probe, scsi_alloc_sdev is called. It calls
    >>scsi_adjust_queue_depth with the cmd_per_lun value.
    >>scsi_adjust_queue_depth returns without doing anything if the tags value
    >>is greater than 256. This leaves the Scsi_Device queue_depth at zero.
    >>Later when an I/O is queued, scsi_request_fn checks for device_busy >=
    >>queue_depth. If so, the function does a break and exits. This is where
    >>it hangs.
    >>To get things to load I set cmd_per_lun to 256. I don't know if the is
    >>the correct way to deal with the problem. Maybe someone else can say
    >>something about that.
    > If the SCSI layer is trying to be clever by ignoring the requested 512
    > then thats the actual problem. 512 is the right value because its not
    > really a disk you are talking to on the main channel. So the scsi layer
    > ought to honour it.

    Here is the relevant code snippet in scsi.c around line

    void scsi_adjust_queue_depth(Scsi_Device *SDpnt, int tagged, int tags)
    static spinlock_t device_request_lock = SPIN_LOCK_UNLOCKED;
    unsigned long flags;

    * refuse to set tagged depth to an unworkable size
    if(tags <= 0)
    * Limit max queue depth on a single lun to 256 for now. Remember,
    * we allocate a struct scsi_command for each of these and keep it
    * around forever. Too deep of a depth just wastes memory.
    if(tags > 256)

    [pardon the wrap]
    Now scsi_device::queue_depth is an unsigned short so that
    is not a problem. Also the comment prior to the
    "if (tags > 256)" is no longer correct (I think). So
    perhaps it can be changed to "if (tags > 65535) ..."

    Doug Gilbert

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