[PATCH 2/9] scsi: avoid taking host_lock in scsi_run_queue unless nessecary

Christoph Hellwig
2014-02-20T22:23:57Z

[-- Attachment #1: 0002-scsi-avoid-taking-host_lock-in-scsi_run_queue-unless.patch --]
[-- Type: text/plain, Size: 2111 bytes --]

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>
---
drivers/scsi/scsi_lib.c | 43 ++++++++++++++++++++++++-------------------
1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 7bd7f0d..ad516c0 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -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);
}
--
1.7.10.4