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/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d0bd7e0..1ddf0fb 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -302,9 +302,7 @@
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 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 @@
* 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 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 @@
* 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 @@
* 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 @@
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 @@
*/
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 @@
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);
}