[SCSI] avoid taking host_lock in scsi_run_queue unless nessecary
authorChristoph Hellwig <hch@infradead.org>
Thu, 20 Feb 2014 22:20:54 +0000 (14:20 -0800)
committerJames Bottomley <JBottomley@Parallels.com>
Sat, 15 Mar 2014 17:19:24 +0000 (10:19 -0700)
If we don't have starved devices we don't need to take the host lock
to iterate over them.  Also split the function up to be more clear.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
drivers/scsi/scsi_lib.c

index f97a1a6..492071c 100644 (file)
@@ -385,29 +385,12 @@ static inline int scsi_host_is_busy(struct Scsi_Host *shost)
        return 0;
 }
 
-/*
- * Function:   scsi_run_queue()
- *
- * Purpose:    Select a proper request queue to serve next
- *
- * Arguments:  q       - last request's queue
- *
- * Returns:     Nothing
- *
- * Notes:      The previous command was completely finished, start
- *             a new one if possible.
- */
-static void scsi_run_queue(struct request_queue *q)
+static void scsi_starved_list_run(struct Scsi_Host *shost)
 {
-       struct scsi_device *sdev = q->queuedata;
-       struct Scsi_Host *shost;
        LIST_HEAD(starved_list);
+       struct scsi_device *sdev;
        unsigned long flags;
 
-       shost = sdev->host;
-       if (scsi_target(sdev)->single_lun)
-               scsi_single_lun_run(sdev);
-
        spin_lock_irqsave(shost->host_lock, flags);
        list_splice_init(&shost->starved_list, &starved_list);
 
@@ -459,6 +442,28 @@ static void scsi_run_queue(struct request_queue *q)
        /* put any unprocessed entries back */
        list_splice(&starved_list, &shost->starved_list);
        spin_unlock_irqrestore(shost->host_lock, flags);
+}
+
+/*
+ * Function:   scsi_run_queue()
+ *
+ * Purpose:    Select a proper request queue to serve next
+ *
+ * Arguments:  q       - last request's queue
+ *
+ * Returns:     Nothing
+ *
+ * Notes:      The previous command was completely finished, start
+ *             a new one if possible.
+ */
+static void scsi_run_queue(struct request_queue *q)
+{
+       struct scsi_device *sdev = q->queuedata;
+
+       if (scsi_target(sdev)->single_lun)
+               scsi_single_lun_run(sdev);
+       if (!list_empty(&sdev->host->starved_list))
+               scsi_starved_list_run(sdev->host);
 
        blk_run_queue(q);
 }