scsi: lpfc: reduce locking when updating statistics

Currently, on each io completion, the stats update routine indiscriminately
holds a lock. While holding the adapter-wide lock, checks are made to check
whether status are being tracked. When disabled (the default), the locking
wasted a lot of cycles.

Check for stats enablement before taking the lock.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/lpfc/lpfc_scsi.c

@@ -202,8 +202,8 @@ lpfc_sli4_set_rsp_sgl_last(struct lpfc_hba *phba,
 static void
 lpfc_update_stats(struct lpfc_hba *phba, struct  lpfc_scsi_buf *lpfc_cmd)
 {
-	struct lpfc_rport_data *rdata = lpfc_cmd->rdata;
-	struct lpfc_nodelist *pnode = rdata->pnode;
+	struct lpfc_rport_data *rdata;
+	struct lpfc_nodelist *pnode;
 	struct scsi_cmnd *cmd = lpfc_cmd->pCmd;
 	unsigned long flags;
 	struct Scsi_Host  *shost = cmd->device->host;
@@ -211,17 +211,19 @@ lpfc_update_stats(struct lpfc_hba *phba, struct  lpfc_scsi_buf *lpfc_cmd)
 	unsigned long latency;
 	int i;
 
-	if (cmd->result)
+	if (!vport->stat_data_enabled ||
+	    vport->stat_data_blocked ||
+	    (cmd->result))
 		return;
 
 	latency = jiffies_to_msecs((long)jiffies - (long)lpfc_cmd->start_time);
+	rdata = lpfc_cmd->rdata;
+	pnode = rdata->pnode;
 
 	spin_lock_irqsave(shost->host_lock, flags);
-	if (!vport->stat_data_enabled ||
-		vport->stat_data_blocked ||
-		!pnode ||
-		!pnode->lat_data ||
-		(phba->bucket_type == LPFC_NO_BUCKET)) {
+	if (!pnode ||
+	    !pnode->lat_data ||
+	    (phba->bucket_type == LPFC_NO_BUCKET)) {
 		spin_unlock_irqrestore(shost->host_lock, flags);
 		return;
 	}