diff mbox

[2/3] dm rq: add DM_MAPIO_DELAY_REQUEUE to delay requeue of blk-mq requests

Message ID 1473782495-44128-3-git-send-email-snitzer@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Mike Snitzer Sept. 13, 2016, 4:01 p.m. UTC 
Otherwise blk-mq will immediately dispatch requests that are requeued
via a BLK_MQ_RQ_QUEUE_BUSY return from blk_mq_ops .queue_rq.

Delayed requeue is implemented using blk_mq_delay_kick_requeue_list()
with a delay of 5 secs.  In the context of DM multipath (all paths down)
it doesn't make any sense to requeue more quickly.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/md/dm-rq.c            | 35 ++++++++++++++++++++---------------
 include/linux/device-mapper.h |  1 +
 2 files changed, 21 insertions(+), 15 deletions(-)

Comments

Hannes Reinecke Sept. 14, 2016, 6:24 a.m. UTC | #1 
On 09/13/2016 06:01 PM, Mike Snitzer wrote:
> Otherwise blk-mq will immediately dispatch requests that are requeued
> via a BLK_MQ_RQ_QUEUE_BUSY return from blk_mq_ops .queue_rq.
> 
> Delayed requeue is implemented using blk_mq_delay_kick_requeue_list()
> with a delay of 5 secs.  In the context of DM multipath (all paths down)
> it doesn't make any sense to requeue more quickly.
> 
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> ---
>  drivers/md/dm-rq.c            | 35 ++++++++++++++++++++---------------
>  include/linux/device-mapper.h |  1 +
>  2 files changed, 21 insertions(+), 15 deletions(-)
> 
Hmm. Not sure if I agree with the reasoning for a 5 seconds delay; this
seems to be a rather broad estimate.
Won't it delay I/O resumption when we have intermittent path failure (eg
on iSCSI)?

Cheers,

Hannes
Mike Snitzer Sept. 14, 2016, 1:51 p.m. UTC | #2 
On Wed, Sep 14 2016 at  2:24am -0400,
Hannes Reinecke <hare@suse.de> wrote:

> On 09/13/2016 06:01 PM, Mike Snitzer wrote:
> > Otherwise blk-mq will immediately dispatch requests that are requeued
> > via a BLK_MQ_RQ_QUEUE_BUSY return from blk_mq_ops .queue_rq.
> > 
> > Delayed requeue is implemented using blk_mq_delay_kick_requeue_list()
> > with a delay of 5 secs.  In the context of DM multipath (all paths down)
> > it doesn't make any sense to requeue more quickly.
> > 
> > Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> > ---
> >  drivers/md/dm-rq.c            | 35 ++++++++++++++++++++---------------
> >  include/linux/device-mapper.h |  1 +
> >  2 files changed, 21 insertions(+), 15 deletions(-)
> > 
> Hmm. Not sure if I agree with the reasoning for a 5 seconds delay; this
> seems to be a rather broad estimate.
> Won't it delay I/O resumption when we have intermittent path failure (eg
> on iSCSI)?

Are you saying the path would be reinstated via the 'reinstate_path'
message or by table reload?  Table reload will kick the requeue list.
'reinstate_path' doesn't (and there isn't an easy way to have dm-mpath
inform dm-rq core to do so -- could add a new function...)

If I can wire up requeue list kick on reinstate_path then the 5 secs is
perfectly fine and won't hurt how quickly IO is resumed once a path
comes back.
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diff mbox

Patch

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 0d301d5..1722220 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -336,21 +336,23 @@  static void dm_old_requeue_request(struct request *rq)
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
-static void dm_mq_requeue_request(struct request *rq)
+static void dm_mq_delay_requeue_request(struct request *rq, unsigned long msecs)
 {
 	struct request_queue *q = rq->q;
 	unsigned long flags;
 
 	blk_mq_requeue_request(rq);
+
 	spin_lock_irqsave(q->queue_lock, flags);
 	if (!blk_queue_stopped(q))
-		blk_mq_kick_requeue_list(q);
+		blk_mq_delay_kick_requeue_list(q, msecs);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
-static void dm_requeue_original_request(struct mapped_device *md,
-					struct request *rq)
+static void dm_requeue_original_request(struct dm_rq_target_io *tio, bool delay_requeue)
 {
+	struct mapped_device *md = tio->md;
+	struct request *rq = tio->orig;
 	int rw = rq_data_dir(rq);
 
 	rq_end_stats(md, rq);
@@ -359,7 +361,7 @@  static void dm_requeue_original_request(struct mapped_device *md,
 	if (!rq->q->mq_ops)
 		dm_old_requeue_request(rq);
 	else
-		dm_mq_requeue_request(rq);
+		dm_mq_delay_requeue_request(rq, delay_requeue ? 5000 : 0);
 
 	rq_completed(md, rw, false);
 }
@@ -389,7 +391,7 @@  static void dm_done(struct request *clone, int error, bool mapped)
 		return;
 	else if (r == DM_ENDIO_REQUEUE)
 		/* The target wants to requeue the I/O */
-		dm_requeue_original_request(tio->md, tio->orig);
+		dm_requeue_original_request(tio, false);
 	else {
 		DMWARN("unimplemented target endio return value: %d", r);
 		BUG();
@@ -629,8 +631,8 @@  static int dm_old_prep_fn(struct request_queue *q, struct request *rq)
 
 /*
  * Returns:
- * 0                : the request has been processed
- * DM_MAPIO_REQUEUE : the original request needs to be requeued
+ * DM_MAPIO_*       : the request has been processed as indicated
+ * DM_MAPIO_REQUEUE : the original request needs to be immediately requeued
  * < 0              : the request was completed due to failure
  */
 static int map_request(struct dm_rq_target_io *tio, struct request *rq,
@@ -643,6 +645,8 @@  static int map_request(struct dm_rq_target_io *tio, struct request *rq,
 	if (tio->clone) {
 		clone = tio->clone;
 		r = ti->type->map_rq(ti, clone, &tio->info);
+		if (r == DM_MAPIO_DELAY_REQUEUE)
+			return DM_MAPIO_REQUEUE; /* .request_fn requeue is always immediate */
 	} else {
 		r = ti->type->clone_and_map_rq(ti, rq, &tio->info, &clone);
 		if (r < 0) {
@@ -650,9 +654,8 @@  static int map_request(struct dm_rq_target_io *tio, struct request *rq,
 			dm_kill_unmapped_request(rq, r);
 			return r;
 		}
-		if (r != DM_MAPIO_REMAPPED)
-			return r;
-		if (setup_clone(clone, rq, tio, GFP_ATOMIC)) {
+		if (r == DM_MAPIO_REMAPPED &&
+		    setup_clone(clone, rq, tio, GFP_ATOMIC)) {
 			/* -ENOMEM */
 			ti->type->release_clone_rq(clone);
 			return DM_MAPIO_REQUEUE;
@@ -671,7 +674,10 @@  static int map_request(struct dm_rq_target_io *tio, struct request *rq,
 		break;
 	case DM_MAPIO_REQUEUE:
 		/* The target wants to requeue the I/O */
-		dm_requeue_original_request(md, tio->orig);
+		break;
+	case DM_MAPIO_DELAY_REQUEUE:
+		/* The target wants to requeue the I/O after a delay */
+		dm_requeue_original_request(tio, true);
 		break;
 	default:
 		if (r > 0) {
@@ -681,10 +687,9 @@  static int map_request(struct dm_rq_target_io *tio, struct request *rq,
 
 		/* The target wants to complete the I/O */
 		dm_kill_unmapped_request(rq, r);
-		return r;
 	}
 
-	return 0;
+	return r;
 }
 
 static void dm_start_request(struct mapped_device *md, struct request *orig)
@@ -727,7 +732,7 @@  static void map_tio_request(struct kthread_work *work)
 	struct mapped_device *md = tio->md;
 
 	if (map_request(tio, rq, md) == DM_MAPIO_REQUEUE)
-		dm_requeue_original_request(md, rq);
+		dm_requeue_original_request(tio, false);
 }
 
 ssize_t dm_attr_rq_based_seq_io_merge_deadline_show(struct mapped_device *md, char *buf)
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 91acfce..ef7962e 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -590,6 +590,7 @@  extern struct ratelimit_state dm_ratelimit_state;
 #define DM_MAPIO_SUBMITTED	0
 #define DM_MAPIO_REMAPPED	1
 #define DM_MAPIO_REQUEUE	DM_ENDIO_REQUEUE
+#define DM_MAPIO_DELAY_REQUEUE	3
 
 #define dm_sector_div64(x, y)( \
 { \