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Date: Sat, 22 Jan 2011 01:17:22 +0000
From: Jens Axboe <jaxboe@...ionio.com>
To: jaxboe@...ionio.com, linux-kernel@...r.kernel.org
Cc: hch@...radead.org
Subject: [PATCH 03/10] scsi: convert to blk_delay_queue()
Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
---
drivers/scsi/scsi_lib.c | 44 +++++++++++++++++++-------------------------
1 files changed, 19 insertions(+), 25 deletions(-)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9045c52..5a0ae7a 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -67,6 +67,13 @@ static struct scsi_host_sg_pool scsi_sg_pools[] = {
struct kmem_cache *scsi_sdb_cache;
+/*
+ * When to reinvoke queueing after a resource shortage. It's 3 msecs to
+ * not change behaviour from the previous unplug mechanism, experimentation
+ * may prove this needs changing.
+ */
+#define SCSI_QUEUE_DELAY 3
+
static void scsi_run_queue(struct request_queue *q);
/*
@@ -149,14 +156,7 @@ static int __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
/*
* Requeue this command. It will go before all other commands
* that are already in the queue.
- *
- * NOTE: there is magic here about the way the queue is plugged if
- * we have no outstanding commands.
- *
- * Although we *don't* plug the queue, we call the request
- * function. The SCSI request function detects the blocked condition
- * and plugs the queue appropriately.
- */
+ */
spin_lock_irqsave(q->queue_lock, flags);
blk_requeue_request(q, cmd->request);
spin_unlock_irqrestore(q->queue_lock, flags);
@@ -1194,11 +1194,11 @@ int scsi_prep_return(struct request_queue *q, struct request *req, int ret)
case BLKPREP_DEFER:
/*
* If we defer, the blk_peek_request() returns NULL, but the
- * queue must be restarted, so we plug here if no returning
- * command will automatically do that.
+ * queue must be restarted, so we schedule a callback to happen
+ * shortly.
*/
if (sdev->device_busy == 0)
- blk_plug_device(q);
+ blk_delay_queue(q, SCSI_QUEUE_DELAY);
break;
default:
req->cmd_flags |= REQ_DONTPREP;
@@ -1237,7 +1237,7 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
sdev_printk(KERN_INFO, sdev,
"unblocking device at zero depth\n"));
} else {
- blk_plug_device(q);
+ blk_delay_queue(q, SCSI_QUEUE_DELAY);
return 0;
}
}
@@ -1467,7 +1467,7 @@ static void scsi_request_fn(struct request_queue *q)
* the host is no longer able to accept any more requests.
*/
shost = sdev->host;
- while (!blk_queue_plugged(q)) {
+ for (;;) {
int rtn;
/*
* get next queueable request. We do this early to make sure
@@ -1546,15 +1546,8 @@ static void scsi_request_fn(struct request_queue *q)
*/
rtn = scsi_dispatch_cmd(cmd);
spin_lock_irq(q->queue_lock);
- if(rtn) {
- /* we're refusing the command; because of
- * the way locks get dropped, we need to
- * check here if plugging is required */
- if(sdev->device_busy == 0)
- blk_plug_device(q);
-
- break;
- }
+ if (rtn)
+ goto out_delay;
}
goto out;
@@ -1573,9 +1566,10 @@ static void scsi_request_fn(struct request_queue *q)
spin_lock_irq(q->queue_lock);
blk_requeue_request(q, req);
sdev->device_busy--;
- if(sdev->device_busy == 0)
- blk_plug_device(q);
- out:
+out_delay:
+ if (sdev->device_busy == 0)
+ blk_delay_queue(q, SCSI_QUEUE_DELAY);
+out:
/* must be careful here...if we trigger the ->remove() function
* we cannot be holding the q lock */
spin_unlock_irq(q->queue_lock);
--
1.7.3.2.146.gca209
--
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