hpsa: count passthru cmds with atomics, not a spin locked int

Performance enhancement. Remove spin_locks from the driver.

Reviewed-by: Scott Teel <scott.teel@pmcs.com>
Signed-off-by: Don Brace <don.brace@pmcs.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

2 files changed, 6 insertions, 36 deletions

diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
index 72abcf3bfabf..bae3759e30e2 100644
--- a/drivers/scsi/hpsa.c
+++ b/drivers/scsi/hpsa.c
@@ -5105,35 +5105,6 @@ static void check_ioctl_unit_attention(struct ctlr_info *h,
                 (void) check_for_unit_attention(h, c);
 }
 
-static int increment_passthru_count(struct ctlr_info *h)
-{
-        unsigned long flags;
-
-        spin_lock_irqsave(&h->passthru_count_lock, flags);
-        if (h->passthru_count >= HPSA_MAX_CONCURRENT_PASSTHRUS) {
-                spin_unlock_irqrestore(&h->passthru_count_lock, flags);
-                return -1;
-        }
-        h->passthru_count++;
-        spin_unlock_irqrestore(&h->passthru_count_lock, flags);
-        return 0;
-}
-
-static void decrement_passthru_count(struct ctlr_info *h)
-{
-        unsigned long flags;
-
-        spin_lock_irqsave(&h->passthru_count_lock, flags);
-        if (h->passthru_count <= 0) {
-                spin_unlock_irqrestore(&h->passthru_count_lock, flags);
-                /* not expecting to get here. */
-                dev_warn(&h->pdev->dev, "Bug detected, passthru_count seems to be incorrect.\n");
-                return;
-        }
-        h->passthru_count--;
-        spin_unlock_irqrestore(&h->passthru_count_lock, flags);
-}
-
 /*
  * ioctl
  */
@@ -5156,16 +5127,16 @@ static int hpsa_ioctl(struct scsi_device *dev, int cmd, void __user *arg)
         case CCISS_GETDRIVVER:
                 return hpsa_getdrivver_ioctl(h, argp);
         case CCISS_PASSTHRU:
-                if (increment_passthru_count(h))
+                if (atomic_dec_if_positive(&h->passthru_cmds_avail) < 0)
                         return -EAGAIN;
                 rc = hpsa_passthru_ioctl(h, argp);
-                decrement_passthru_count(h);
+                atomic_inc(&h->passthru_cmds_avail);
                 return rc;
         case CCISS_BIG_PASSTHRU:
-                if (increment_passthru_count(h))
+                if (atomic_dec_if_positive(&h->passthru_cmds_avail) < 0)
                         return -EAGAIN;
                 rc = hpsa_big_passthru_ioctl(h, argp);
-                decrement_passthru_count(h);
+                atomic_inc(&h->passthru_cmds_avail);
                 return rc;
         default:
                 return -ENOTTY;
@@ -6852,7 +6823,7 @@ reinit_after_soft_reset:
         spin_lock_init(&h->lock);
         spin_lock_init(&h->offline_device_lock);
         spin_lock_init(&h->scan_lock);
-        spin_lock_init(&h->passthru_count_lock);
+        atomic_set(&h->passthru_cmds_avail, HPSA_MAX_CONCURRENT_PASSTHRUS);
 
         h->resubmit_wq = alloc_workqueue("hpsa", WQ_MEM_RECLAIM, 0);
         if (!h->resubmit_wq) {
diff --git a/drivers/scsi/hpsa.h b/drivers/scsi/hpsa.h
index 981479a13935..1856445f883a 100644
--- a/drivers/scsi/hpsa.h
+++ b/drivers/scsi/hpsa.h
@@ -183,8 +183,7 @@ struct ctlr_info {
 
         /* cap concurrent passthrus at some reasonable maximum */
 #define HPSA_MAX_CONCURRENT_PASSTHRUS (10)
-        spinlock_t passthru_count_lock; /* protects passthru_count */
-        int passthru_count;
+        atomic_t passthru_cmds_avail;
 
         /*
          * Performant mode completion buffers