scsi: only maintain target_blocked if the driver has a target queue limit

This saves us an atomic operation for each I/O submission and completion
for the usual case where the driver doesn't set a per-target can_queue
value.  Only a few iscsi hardware offload drivers set the per-target
can_queue value at the moment.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Webb Scales <webbnh@hp.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Robert Elliott <elliott@hp.com>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 69da4cb5cb13453af6a27b044fa1d9c9457eb855..a643353584b54dbac01d232ba920bdd454e62dce 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -295,7 +295,8 @@ void scsi_device_unbusy(struct scsi_device *sdev)
        unsigned long flags;
 
        atomic_dec(&shost->host_busy);
-       atomic_dec(&starget->target_busy);
+       if (starget->can_queue > 0)
+               atomic_dec(&starget->target_busy);
 
        if (unlikely(scsi_host_in_recovery(shost) &&
                     (shost->host_failed || shost->host_eh_scheduled))) {
@@ -364,11 +365,12 @@ static inline bool scsi_device_is_busy(struct scsi_device *sdev)
 
 static inline bool scsi_target_is_busy(struct scsi_target *starget)
 {
-       if (starget->can_queue > 0 &&
-           atomic_read(&starget->target_busy) >= starget->can_queue)
-               return true;
-       if (atomic_read(&starget->target_blocked) > 0)
-               return true;
+       if (starget->can_queue > 0) {
+               if (atomic_read(&starget->target_busy) >= starget->can_queue)
+                       return true;
+               if (atomic_read(&starget->target_blocked) > 0)
+                       return true;
+       }
        return false;
 }
 
@@ -1309,6 +1311,9 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
                spin_unlock_irq(shost->host_lock);
        }
 
+       if (starget->can_queue <= 0)
+               return 1;
+
        busy = atomic_inc_return(&starget->target_busy) - 1;
        if (atomic_read(&starget->target_blocked) > 0) {
                if (busy)
@@ -1324,7 +1329,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
                                 "unblocking target at zero depth\n"));
        }
 
-       if (starget->can_queue > 0 && busy >= starget->can_queue)
+       if (busy >= starget->can_queue)
                goto starved;
 
        return 1;
@@ -1334,7 +1339,8 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
        list_move_tail(&sdev->starved_entry, &shost->starved_list);
        spin_unlock_irq(shost->host_lock);
 out_dec:
-       atomic_dec(&starget->target_busy);
+       if (starget->can_queue > 0)
+               atomic_dec(&starget->target_busy);
        return 0;
 }
 
@@ -1455,7 +1461,8 @@ static void scsi_kill_request(struct request *req, struct request_queue *q)
         */
        atomic_inc(&sdev->device_busy);
        atomic_inc(&shost->host_busy);
-       atomic_inc(&starget->target_busy);
+       if (starget->can_queue > 0)
+               atomic_inc(&starget->target_busy);
 
        blk_complete_request(req);
 }
@@ -1624,7 +1631,8 @@ static void scsi_request_fn(struct request_queue *q)
        return;
 
  host_not_ready:
-       atomic_dec(&scsi_target(sdev)->target_busy);
+       if (scsi_target(sdev)->can_queue > 0)
+               atomic_dec(&scsi_target(sdev)->target_busy);
  not_ready:
        /*
         * lock q, handle tag, requeue req, and decrement device_busy. We