scsi: convert device_busy to atomic_t

Avoid taking the queue_lock to check the per-device queue limit.  Instead
we do an atomic_inc_return early on to grab our slot in the queue,
and if necessary decrement it after finishing all checks.

Unlike the host and target busy counters this doesn't allow us to avoid the
queue_lock in the request_fn due to the way the interface works, but it'll
allow us to prepare for using the blk-mq code, which doesn't use the
queue_lock at all, and it at least avoids a queue_lock round trip in
scsi_device_unbusy, which is still important given how busy the queue_lock
is.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
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/message/fusion/mptsas.c b/drivers/message/fusion/mptsas.c
index 711fcb5cec8750556de23248aa424af5f4deb084..d636dbe172a3cf4a34cfc8b00cedd4f96582c6ea 100644 (file)
--- a/drivers/message/fusion/mptsas.c
+++ b/drivers/message/fusion/mptsas.c
@@ -3763,7 +3763,7 @@ mptsas_send_link_status_event(struct fw_event_work *fw_event)
                                                printk(MYIOC_s_DEBUG_FMT
                                                "SDEV OUTSTANDING CMDS"
                                                "%d\n", ioc->name,
-                                               sdev->device_busy));
+                                               atomic_read(&sdev->device_busy)));
                                }
 
                        }

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d0bd7e0ab7a8874af59d2d74eb1720b869c16208..1ddf0fb43b595a75fa2313a4776684b96824150f 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -302,9 +302,7 @@ void scsi_device_unbusy(struct scsi_device *sdev)
                spin_unlock_irqrestore(shost->host_lock, flags);
        }
 
-       spin_lock_irqsave(sdev->request_queue->queue_lock, flags);
-       sdev->device_busy--;
-       spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
+       atomic_dec(&sdev->device_busy);
 }
 
 /*
@@ -355,9 +353,9 @@ static void scsi_single_lun_run(struct scsi_device *current_sdev)
 
 static inline int scsi_device_is_busy(struct scsi_device *sdev)
 {
-       if (sdev->device_busy >= sdev->queue_depth || sdev->device_blocked)
+       if (atomic_read(&sdev->device_busy) >= sdev->queue_depth ||
+           sdev->device_blocked)
                return 1;
-
        return 0;
 }
 
@@ -1204,7 +1202,7 @@ scsi_prep_return(struct request_queue *q, struct request *req, int ret)
                 * queue must be restarted, so we schedule a callback to happen
                 * shortly.
                 */
-               if (sdev->device_busy == 0)
+               if (atomic_read(&sdev->device_busy) == 0)
                        blk_delay_queue(q, SCSI_QUEUE_DELAY);
                break;
        default:
@@ -1255,26 +1253,33 @@ static void scsi_unprep_fn(struct request_queue *q, struct request *req)
 static inline int scsi_dev_queue_ready(struct request_queue *q,
                                  struct scsi_device *sdev)
 {
-       if (sdev->device_busy == 0 && sdev->device_blocked) {
+       unsigned int busy;
+
+       busy = atomic_inc_return(&sdev->device_busy) - 1;
+       if (sdev->device_blocked) {
+               if (busy)
+                       goto out_dec;
+
                /*
                 * unblock after device_blocked iterates to zero
                 */
-               if (--sdev->device_blocked == 0) {
-                       SCSI_LOG_MLQUEUE(3,
-                                  sdev_printk(KERN_INFO, sdev,
-                                  "unblocking device at zero depth\n"));
-               } else {
+               if (--sdev->device_blocked != 0) {
                        blk_delay_queue(q, SCSI_QUEUE_DELAY);
-                       return 0;
+                       goto out_dec;
                }
+               SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
+                                  "unblocking device at zero depth\n"));
        }
-       if (scsi_device_is_busy(sdev))
-               return 0;
+
+       if (busy >= sdev->queue_depth)
+               goto out_dec;
 
        return 1;
+out_dec:
+       atomic_dec(&sdev->device_busy);
+       return 0;
 }
 
-
 /*
  * scsi_target_queue_ready: checks if there we can send commands to target
  * @sdev: scsi device on starget to check.
@@ -1448,7 +1453,7 @@ static void scsi_kill_request(struct request *req, struct request_queue *q)
         * bump busy counts.  To bump the counters, we need to dance
         * with the locks as normal issue path does.
         */
-       sdev->device_busy++;
+       atomic_inc(&sdev->device_busy);
        atomic_inc(&shost->host_busy);
        atomic_inc(&starget->target_busy);
 
@@ -1544,7 +1549,7 @@ static void scsi_request_fn(struct request_queue *q)
                 * accept it.
                 */
                req = blk_peek_request(q);
-               if (!req || !scsi_dev_queue_ready(q, sdev))
+               if (!req)
                        break;
 
                if (unlikely(!scsi_device_online(sdev))) {
@@ -1554,13 +1559,14 @@ static void scsi_request_fn(struct request_queue *q)
                        continue;
                }
 
+               if (!scsi_dev_queue_ready(q, sdev))
+                       break;
 
                /*
                 * Remove the request from the request list.
                 */
                if (!(blk_queue_tagged(q) && !blk_queue_start_tag(q, req)))
                        blk_start_request(req);
-               sdev->device_busy++;
 
                spin_unlock_irq(q->queue_lock);
                cmd = req->special;
@@ -1630,9 +1636,9 @@ static void scsi_request_fn(struct request_queue *q)
         */
        spin_lock_irq(q->queue_lock);
        blk_requeue_request(q, req);
-       sdev->device_busy--;
+       atomic_dec(&sdev->device_busy);
 out_delay:
-       if (sdev->device_busy == 0 && !scsi_device_blocked(sdev))
+       if (atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev))
                blk_delay_queue(q, SCSI_QUEUE_DELAY);
 }
 
@@ -2371,7 +2377,7 @@ scsi_device_quiesce(struct scsi_device *sdev)
                return err;
 
        scsi_run_queue(sdev->request_queue);
-       while (sdev->device_busy) {
+       while (atomic_read(&sdev->device_busy)) {
                msleep_interruptible(200);
                scsi_run_queue(sdev->request_queue);
        }

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index de57b8bca7be111abc02874e034ff538c3ee1e1c..79df9847edefa6537430aa1ab8e12001e48cdccb 100644 (file)
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -585,13 +585,21 @@ static int scsi_sdev_check_buf_bit(const char *buf)
  * Create the actual show/store functions and data structures.
  */
 sdev_rd_attr (device_blocked, "%d\n");
-sdev_rd_attr (device_busy, "%d\n");
 sdev_rd_attr (type, "%d\n");
 sdev_rd_attr (scsi_level, "%d\n");
 sdev_rd_attr (vendor, "%.8s\n");
 sdev_rd_attr (model, "%.16s\n");
 sdev_rd_attr (rev, "%.4s\n");
 
+static ssize_t
+sdev_show_device_busy(struct device *dev, struct device_attribute *attr,
+               char *buf)
+{
+       struct scsi_device *sdev = to_scsi_device(dev);
+       return snprintf(buf, 20, "%d\n", atomic_read(&sdev->device_busy));
+}
+static DEVICE_ATTR(device_busy, S_IRUGO, sdev_show_device_busy, NULL);
+
 /*
  * TODO: can we make these symlinks to the block layer ones?
  */

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 7a291f5c7227b4a30880d0b88f3159b06437341c..01cf88888797898de231bc9a8dac484be598ee6a 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -2574,7 +2574,7 @@ static int sg_proc_seq_show_dev(struct seq_file *s, void *v)
                              scsidp->id, scsidp->lun, (int) scsidp->type,
                              1,
                              (int) scsidp->queue_depth,
-                             (int) scsidp->device_busy,
+                             (int) atomic_read(&scsidp->device_busy),
                              (int) scsi_device_online(scsidp));
        }
        read_unlock_irqrestore(&sg_index_lock, iflags);

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 4e078b63a9e5f655eda6b1e71c885e96f5aed6b5..3329901c72431d5da127d57231365fde3391286f 100644 (file)
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -81,9 +81,7 @@ struct scsi_device {
        struct list_head    siblings;   /* list of all devices on this host */
        struct list_head    same_target_siblings; /* just the devices sharing same target id */
 
-       /* this is now protected by the request_queue->queue_lock */
-       unsigned int device_busy;       /* commands actually active on
-                                        * low-level. protected by queue_lock. */
+       atomic_t device_busy;           /* commands actually active on LLDD */
        spinlock_t list_lock;
        struct list_head cmd_list;      /* queue of in use SCSI Command structures */
        struct list_head starved_entry;