scsi: convert host_busy to atomic_t
Avoid taking the host-wide host_lock to check the per-host 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 0580711..d0bd7e0 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -292,14 +292,17 @@
struct scsi_target *starget = scsi_target(sdev);
unsigned long flags;
- spin_lock_irqsave(shost->host_lock, flags);
- shost->host_busy--;
+ atomic_dec(&shost->host_busy);
atomic_dec(&starget->target_busy);
+
if (unlikely(scsi_host_in_recovery(shost) &&
- (shost->host_failed || shost->host_eh_scheduled)))
+ (shost->host_failed || shost->host_eh_scheduled))) {
+ spin_lock_irqsave(shost->host_lock, flags);
scsi_eh_wakeup(shost);
- spin_unlock(shost->host_lock);
- spin_lock(sdev->request_queue->queue_lock);
+ 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);
}
@@ -367,7 +370,8 @@
static inline int scsi_host_is_busy(struct Scsi_Host *shost)
{
- if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
+ if ((shost->can_queue > 0 &&
+ atomic_read(&shost->host_busy) >= shost->can_queue) ||
shost->host_blocked || shost->host_self_blocked)
return 1;
@@ -1334,38 +1338,54 @@
struct Scsi_Host *shost,
struct scsi_device *sdev)
{
- int ret = 0;
-
- spin_lock_irq(shost->host_lock);
+ unsigned int busy;
if (scsi_host_in_recovery(shost))
- goto out;
- if (shost->host_busy == 0 && shost->host_blocked) {
+ return 0;
+
+ busy = atomic_inc_return(&shost->host_busy) - 1;
+ if (shost->host_blocked) {
+ if (busy)
+ goto starved;
+
/*
* unblock after host_blocked iterates to zero
*/
- if (--shost->host_blocked != 0)
- goto out;
+ spin_lock_irq(shost->host_lock);
+ if (--shost->host_blocked != 0) {
+ spin_unlock_irq(shost->host_lock);
+ goto out_dec;
+ }
+ spin_unlock_irq(shost->host_lock);
SCSI_LOG_MLQUEUE(3,
shost_printk(KERN_INFO, shost,
"unblocking host at zero depth\n"));
}
- if (scsi_host_is_busy(shost)) {
- if (list_empty(&sdev->starved_entry))
- list_add_tail(&sdev->starved_entry, &shost->starved_list);
- goto out;
- }
+
+ if (shost->can_queue > 0 && busy >= shost->can_queue)
+ goto starved;
+ if (shost->host_self_blocked)
+ goto starved;
/* We're OK to process the command, so we can't be starved */
- if (!list_empty(&sdev->starved_entry))
- list_del_init(&sdev->starved_entry);
+ if (!list_empty(&sdev->starved_entry)) {
+ spin_lock_irq(shost->host_lock);
+ if (!list_empty(&sdev->starved_entry))
+ list_del_init(&sdev->starved_entry);
+ spin_unlock_irq(shost->host_lock);
+ }
- shost->host_busy++;
- ret = 1;
-out:
+ return 1;
+
+starved:
+ spin_lock_irq(shost->host_lock);
+ if (list_empty(&sdev->starved_entry))
+ list_add_tail(&sdev->starved_entry, &shost->starved_list);
spin_unlock_irq(shost->host_lock);
- return ret;
+out_dec:
+ atomic_dec(&shost->host_busy);
+ return 0;
}
/*
@@ -1429,12 +1449,8 @@
* with the locks as normal issue path does.
*/
sdev->device_busy++;
- spin_unlock(sdev->request_queue->queue_lock);
- spin_lock(shost->host_lock);
- shost->host_busy++;
+ atomic_inc(&shost->host_busy);
atomic_inc(&starget->target_busy);
- spin_unlock(shost->host_lock);
- spin_lock(sdev->request_queue->queue_lock);
blk_complete_request(req);
}