1 files changed, 33 insertions, 3 deletions

diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c
index d0df1b2faf2..46973d6618d 100644
--- a/drivers/scsi/libfc/fc_exch.c
+++ b/drivers/scsi/libfc/fc_exch.c
@@ -67,6 +67,11 @@ struct workqueue_struct *fc_exch_workqueue;
 struct fc_exch_pool {
 	u16		 next_index;
 	u16		 total_exches;
+
+	/* two cache of free slot in exch array */
+	u16		 left;
+	u16		 right;
+
 	spinlock_t	 lock;
 	struct list_head ex_list;
 };
@@ -396,13 +401,23 @@ static inline void fc_exch_ptr_set(struct fc_exch_pool *pool, u16 index,
 static void fc_exch_delete(struct fc_exch *ep)
 {
 	struct fc_exch_pool *pool;
+	u16 index;
 
 	pool = ep->pool;
 	spin_lock_bh(&pool->lock);
 	WARN_ON(pool->total_exches <= 0);
 	pool->total_exches--;
-	fc_exch_ptr_set(pool, (ep->xid - ep->em->min_xid) >> fc_cpu_order,
-			NULL);
+
+	/* update cache of free slot */
+	index = (ep->xid - ep->em->min_xid) >> fc_cpu_order;
+	if (pool->left == FC_XID_UNKNOWN)
+		pool->left = index;
+	else if (pool->right == FC_XID_UNKNOWN)
+		pool->right = index;
+	else
+		pool->next_index = index;
+
+	fc_exch_ptr_set(pool, index, NULL);
 	list_del(&ep->ex_list);
 	spin_unlock_bh(&pool->lock);
 	fc_exch_release(ep);	/* drop hold for exch in mp */
@@ -678,6 +693,19 @@ static struct fc_exch *fc_exch_em_alloc(struct fc_lport *lport,
 	pool = per_cpu_ptr(mp->pool, cpu);
 	spin_lock_bh(&pool->lock);
 	put_cpu();
+
+	/* peek cache of free slot */
+	if (pool->left != FC_XID_UNKNOWN) {
+		index = pool->left;
+		pool->left = FC_XID_UNKNOWN;
+		goto hit;
+	}
+	if (pool->right != FC_XID_UNKNOWN) {
+		index = pool->right;
+		pool->right = FC_XID_UNKNOWN;
+		goto hit;
+	}
+
 	index = pool->next_index;
 	/* allocate new exch from pool */
 	while (fc_exch_ptr_get(pool, index)) {
@@ -686,7 +714,7 @@ static struct fc_exch *fc_exch_em_alloc(struct fc_lport *lport,
 			goto err;
 	}
 	pool->next_index = index == mp->pool_max_index ? 0 : index + 1;
-
+hit:
 	fc_exch_hold(ep);	/* hold for exch in mp */
 	spin_lock_init(&ep->ex_lock);
 	/*
@@ -2180,6 +2208,8 @@ struct fc_exch_mgr *fc_exch_mgr_alloc(struct fc_lport *lport,
 		goto free_mempool;
 	for_each_possible_cpu(cpu) {
 		pool = per_cpu_ptr(mp->pool, cpu);
+		pool->left = FC_XID_UNKNOWN;
+		pool->right = FC_XID_UNKNOWN;
 		spin_lock_init(&pool->lock);
 		INIT_LIST_HEAD(&pool->ex_list);
 	}