scsi: convert target_busy to an atomic_t
Avoid taking the host-wide host_lock to check the per-target 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.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
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 112c737..0580711 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -294,7 +294,7 @@
spin_lock_irqsave(shost->host_lock, flags);
shost->host_busy--;
- starget->target_busy--;
+ atomic_dec(&starget->target_busy);
if (unlikely(scsi_host_in_recovery(shost) &&
(shost->host_failed || shost->host_eh_scheduled)))
scsi_eh_wakeup(shost);
@@ -361,7 +361,7 @@
static inline int scsi_target_is_busy(struct scsi_target *starget)
{
return ((starget->can_queue > 0 &&
- starget->target_busy >= starget->can_queue) ||
+ atomic_read(&starget->target_busy) >= starget->can_queue) ||
starget->target_blocked);
}
@@ -1279,37 +1279,50 @@
struct scsi_device *sdev)
{
struct scsi_target *starget = scsi_target(sdev);
- int ret = 0;
+ unsigned int busy;
- spin_lock_irq(shost->host_lock);
if (starget->single_lun) {
+ spin_lock_irq(shost->host_lock);
if (starget->starget_sdev_user &&
- starget->starget_sdev_user != sdev)
- goto out;
+ starget->starget_sdev_user != sdev) {
+ spin_unlock_irq(shost->host_lock);
+ return 0;
+ }
starget->starget_sdev_user = sdev;
+ spin_unlock_irq(shost->host_lock);
}
- if (starget->target_busy == 0 && starget->target_blocked) {
+ busy = atomic_inc_return(&starget->target_busy) - 1;
+ if (starget->target_blocked) {
+ if (busy)
+ goto starved;
+
/*
* unblock after target_blocked iterates to zero
*/
- if (--starget->target_blocked != 0)
- goto out;
+ spin_lock_irq(shost->host_lock);
+ if (--starget->target_blocked != 0) {
+ spin_unlock_irq(shost->host_lock);
+ goto out_dec;
+ }
+ spin_unlock_irq(shost->host_lock);
SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
"unblocking target at zero depth\n"));
}
- if (scsi_target_is_busy(starget)) {
- list_move_tail(&sdev->starved_entry, &shost->starved_list);
- goto out;
- }
+ if (starget->can_queue > 0 && busy >= starget->can_queue)
+ goto starved;
- scsi_target(sdev)->target_busy++;
- ret = 1;
-out:
+ return 1;
+
+starved:
+ spin_lock_irq(shost->host_lock);
+ list_move_tail(&sdev->starved_entry, &shost->starved_list);
spin_unlock_irq(shost->host_lock);
- return ret;
+out_dec:
+ atomic_dec(&starget->target_busy);
+ return 0;
}
/*
@@ -1419,7 +1432,7 @@
spin_unlock(sdev->request_queue->queue_lock);
spin_lock(shost->host_lock);
shost->host_busy++;
- starget->target_busy++;
+ atomic_inc(&starget->target_busy);
spin_unlock(shost->host_lock);
spin_lock(sdev->request_queue->queue_lock);
@@ -1589,9 +1602,7 @@
return;
host_not_ready:
- spin_lock_irq(shost->host_lock);
- scsi_target(sdev)->target_busy--;
- spin_unlock_irq(shost->host_lock);
+ atomic_dec(&scsi_target(sdev)->target_busy);
not_ready:
/*
* lock q, handle tag, requeue req, and decrement device_busy. We