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    Subject[PATCH 03/10] scsi: convert to blk_delay_queue()
    Date
    Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
    ---
    drivers/scsi/scsi_lib.c | 44 +++++++++++++++++++-------------------------
    1 files changed, 19 insertions(+), 25 deletions(-)

    diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
    index 9045c52..5a0ae7a 100644
    --- a/drivers/scsi/scsi_lib.c
    +++ b/drivers/scsi/scsi_lib.c
    @@ -67,6 +67,13 @@ static struct scsi_host_sg_pool scsi_sg_pools[] = {

    struct kmem_cache *scsi_sdb_cache;

    +/*
    + * When to reinvoke queueing after a resource shortage. It's 3 msecs to
    + * not change behaviour from the previous unplug mechanism, experimentation
    + * may prove this needs changing.
    + */
    +#define SCSI_QUEUE_DELAY 3
    +
    static void scsi_run_queue(struct request_queue *q);

    /*
    @@ -149,14 +156,7 @@ static int __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
    /*
    * Requeue this command. It will go before all other commands
    * that are already in the queue.
    - *
    - * NOTE: there is magic here about the way the queue is plugged if
    - * we have no outstanding commands.
    - *
    - * Although we *don't* plug the queue, we call the request
    - * function. The SCSI request function detects the blocked condition
    - * and plugs the queue appropriately.
    - */
    + */
    spin_lock_irqsave(q->queue_lock, flags);
    blk_requeue_request(q, cmd->request);
    spin_unlock_irqrestore(q->queue_lock, flags);
    @@ -1194,11 +1194,11 @@ int scsi_prep_return(struct request_queue *q, struct request *req, int ret)
    case BLKPREP_DEFER:
    /*
    * If we defer, the blk_peek_request() returns NULL, but the
    - * queue must be restarted, so we plug here if no returning
    - * command will automatically do that.
    + * queue must be restarted, so we schedule a callback to happen
    + * shortly.
    */
    if (sdev->device_busy == 0)
    - blk_plug_device(q);
    + blk_delay_queue(q, SCSI_QUEUE_DELAY);
    break;
    default:
    req->cmd_flags |= REQ_DONTPREP;
    @@ -1237,7 +1237,7 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
    sdev_printk(KERN_INFO, sdev,
    "unblocking device at zero depth\n"));
    } else {
    - blk_plug_device(q);
    + blk_delay_queue(q, SCSI_QUEUE_DELAY);
    return 0;
    }
    }
    @@ -1467,7 +1467,7 @@ static void scsi_request_fn(struct request_queue *q)
    * the host is no longer able to accept any more requests.
    */
    shost = sdev->host;
    - while (!blk_queue_plugged(q)) {
    + for (;;) {
    int rtn;
    /*
    * get next queueable request. We do this early to make sure
    @@ -1546,15 +1546,8 @@ static void scsi_request_fn(struct request_queue *q)
    */
    rtn = scsi_dispatch_cmd(cmd);
    spin_lock_irq(q->queue_lock);
    - if(rtn) {
    - /* we're refusing the command; because of
    - * the way locks get dropped, we need to
    - * check here if plugging is required */
    - if(sdev->device_busy == 0)
    - blk_plug_device(q);
    -
    - break;
    - }
    + if (rtn)
    + goto out_delay;
    }

    goto out;
    @@ -1573,9 +1566,10 @@ static void scsi_request_fn(struct request_queue *q)
    spin_lock_irq(q->queue_lock);
    blk_requeue_request(q, req);
    sdev->device_busy--;
    - if(sdev->device_busy == 0)
    - blk_plug_device(q);
    - out:
    +out_delay:
    + if (sdev->device_busy == 0)
    + blk_delay_queue(q, SCSI_QUEUE_DELAY);
    +out:
    /* must be careful here...if we trigger the ->remove() function
    * we cannot be holding the q lock */
    spin_unlock_irq(q->queue_lock);
    --
    1.7.3.2.146.gca209


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