fix IO hangs

PATCH In review Nick Piggin 3 participants 7 messages Sep 5, 2003 – Sep 6, 2003 Block layer

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Nick Piggin

author

2003-09-05 06:57 UTC #0 lore raw

PATCH 1/1 fix IO hangs

Hi, sorry for the hangs, everyone. I think I have it worked out, but testers and an ack from Jens would be good.

The insert_here code now does as advertised. The big difference being that regular blk_fs_requests will be subject to it (required for SCSI requeue). Unfortunately ll_rw_blk.c misuses it and will sometimes try to insert at requests which are not on the dispatch list, causing the badness.

It looks like the code was maybe used to provide an insertion hint for the elevator. The RB tree has now eliminated that requirement even if the code did work. Which it doesn't.

I can't reproduce the hangs with this patch. Please test.

Aside, insert_here really seems to be quite dangerous to me. I think combination of barriers and an "insert at start/end" flag would be enough.

drivers/block/ll_rw_blk.c renamed from linux-2.6/drivers/block/ll_rw_blk.c +1 -1

@@ -2060,7 +2060,7 @@ get_rq:
 	req->rq_disk = bio->bi_bdev->bd_disk;
 	req->start_time = jiffies;
 
-	add_request(q, req, insert_here);
+	add_request(q, req, NULL);
 out:
 	if (freereq)
 		__blk_put_request(q, freereq);

Jens Axboe

2003-09-05 07:04 UTC #1 lore raw

Quoted 13 lines · Nick Piggin

Hi, sorry for the hangs, everyone. I think I have it worked out, but testers and an ack from Jens would be good.
The insert_here code now does as advertised. The big difference being that regular blk_fs_requests will be subject to it (required for SCSI requeue). Unfortunately ll_rw_blk.c misuses it and will sometimes try to insert at requests which are not on the dispatch list, causing the badness.
It looks like the code was maybe used to provide an insertion hint for the elevator. The RB tree has now eliminated that requirement even if the code did work. Which it doesn't.

Quoted 6 lines

I can't reproduce the hangs with this patch. Please test.
Aside, insert_here really seems to be quite dangerous to me. I think combination of barriers and an "insert at start/end" flag would be enough.

Please just kill insert_here, it's exceeded its life expectancy. The 2.2 io scheduler did a merge scan followed by an insertion scan, 2.3 collapsed them into one scan as an optimization. Performance oriented io schedulers need to use better data structures.

Best would be to change it to pass a request back even for the NO_MERGE case, if it has found a good insertion point. It's still a good idea to be able to pass hints back like this, as it could still be a viable optimization for _other_ io schedulers.

Signature · 1 line

Jens Axboe

Nick Piggin

author

2003-09-05 07:17 UTC #2 lore raw

Quoted 28 lines · Jens Axboe

Quoted 13 lines · Nick Piggin
Hi, sorry for the hangs, everyone. I think I have it worked out, but testers and an ack from Jens would be good.
The insert_here code now does as advertised. The big difference being that regular blk_fs_requests will be subject to it (required for SCSI requeue). Unfortunately ll_rw_blk.c misuses it and will sometimes try to insert at requests which are not on the dispatch list, causing the badness.
It looks like the code was maybe used to provide an insertion hint for the elevator. The RB tree has now eliminated that requirement even if the code did work. Which it doesn't.
Quoted 7 lines
I can't reproduce the hangs with this patch. Please test.
Aside, insert_here really seems to be quite dangerous to me. I think combination of barriers and an "insert at start/end" flag would be enough.
Please just kill insert_here, it's exceeded its life expectancy. The 2.2 io scheduler did a merge scan followed by an insertion scan, 2.3 collapsed them into one scan as an optimization. Performance oriented io schedulers need to use better data structures.

Quoted 5 lines

Best would be to change it to pass a request back even for the NO_MERGE case, if it has found a good insertion point. It's still a good idea to be able to pass hints back like this, as it could still be a viable optimization for _other_ io schedulers.

OK, that is sort of an ACK! Pending wider testing this patch needs to get in.

Jens, if insert_here is dead, there is no point to passing back a hint because it can't get back to the elevator anyway.

I'd very much like to kill insert_here and be done with it. If another io scheduler comes along with a good use for it then the writers can come up with an elegant solution ;) Hey, if they know a NO_MERGE return means an insert will soon happen under the same lock, they could keep it cached privately.

Jens Axboe

2003-09-05 07:18 UTC #3 lore raw

Quoted 32 lines · Nick Piggin

Quoted 28 lines · Jens Axboe
Quoted 13 lines · Nick Piggin
Hi, sorry for the hangs, everyone. I think I have it worked out, but testers and an ack from Jens would be good.
The insert_here code now does as advertised. The big difference being that regular blk_fs_requests will be subject to it (required for SCSI requeue). Unfortunately ll_rw_blk.c misuses it and will sometimes try to insert at requests which are not on the dispatch list, causing the badness.
It looks like the code was maybe used to provide an insertion hint for the elevator. The RB tree has now eliminated that requirement even if the code did work. Which it doesn't.
Quoted 7 lines
I can't reproduce the hangs with this patch. Please test.
Aside, insert_here really seems to be quite dangerous to me. I think combination of barriers and an "insert at start/end" flag would be enough.
Please just kill insert_here, it's exceeded its life expectancy. The 2.2 io scheduler did a merge scan followed by an insertion scan, 2.3 collapsed them into one scan as an optimization. Performance oriented io schedulers need to use better data structures.

Quoted 8 lines

Quoted 5 lines
Best would be to change it to pass a request back even for the NO_MERGE case, if it has found a good insertion point. It's still a good idea to be able to pass hints back like this, as it could still be a viable optimization for _other_ io schedulers.
OK, that is sort of an ACK! Pending wider testing this patch needs to get in.

Fold it in with your elv-insertion fix and let it test in -mm?

Quoted 8 lines

Jens, if insert_here is dead, there is no point to passing back a hint because it can't get back to the elevator anyway.
I'd very much like to kill insert_here and be done with it. If another io scheduler comes along with a good use for it then the writers can come up with an elegant solution ;) Hey, if they know a NO_MERGE return means an insert will soon happen under the same lock, they could keep it cached privately.

Agree, lets just kill it off.

Signature · 1 line

Jens Axboe

Jens Axboe

2003-09-05 08:31 UTC #4 lore raw

Quoted 10 lines · Jens Axboe

Quoted 8 lines
Jens, if insert_here is dead, there is no point to passing back a hint because it can't get back to the elevator anyway.
I'd very much like to kill insert_here and be done with it. If another io scheduler comes along with a good use for it then the writers can come up with an elegant solution ;) Hey, if they know a NO_MERGE return means an insert will soon happen under the same lock, they could keep it cached privately.
Agree, lets just kill it off.

Here's the patch that kills it and its associated logic off completely. Nick, I'm not too sure what the logic was for stopping anticipation in as_insert_request() (the insert_here tests were somewhat convoluted :), I've added what I think makes most sense: stop anticipating if someone puts a request at the head of the dispatch list.

It also makes the *_insert_request strategies much easier to follow, imo.

===== drivers/block/as-iosched.c 1.16 vs edited =====

drivers/block/as-iosched.c +23 ~~-31~~

@@ -255,7 +255,7 @@
 {
 	as_del_arq_hash(arq);
 
-	if (q->last_merge == &arq->request->queuelist)
+	if (q->last_merge == arq->request)
 		q->last_merge = NULL;
 }

@@ -1347,50 +1347,42 @@
 }
 
 static void
-as_insert_request(request_queue_t *q, struct request *rq,
-			struct list_head *insert_here)
+as_insert_request(request_queue_t *q, struct request *rq, int where)
 {
 	struct as_data *ad = q->elevator.elevator_data;
 	struct as_rq *arq = RQ_DATA(rq);
 
-	if (unlikely(rq->flags & (REQ_HARDBARRIER|REQ_SOFTBARRIER))) {
+	if (unlikely(rq->flags & (REQ_HARDBARRIER|REQ_SOFTBARRIER)))
 		q->last_merge = NULL;
 
-		if (insert_here != ad->dispatch) {
+	switch (where) {
+		case ELEVATOR_INSERT_BACK:
 			while (ad->next_arq[REQ_SYNC])
 				as_move_to_dispatch(ad, ad->next_arq[REQ_SYNC]);
 
 			while (ad->next_arq[REQ_ASYNC])
 				as_move_to_dispatch(ad, ad->next_arq[REQ_ASYNC]);
-		}
-
-		if (!insert_here)
-			insert_here = ad->dispatch->prev;
-	}
-
-	if (unlikely(!blk_fs_request(rq))) {
-		if (!insert_here)
-			insert_here = ad->dispatch;
-	}
-
-	if (insert_here) {
-		list_add(&rq->queuelist, insert_here);
-
-		/* Stop anticipating - let this request get through */
-		if (list_empty(ad->dispatch))
+			list_add_tail(&rq->queuelist, ad->dispatch);
+			break;
+		case ELEVATOR_INSERT_FRONT:
+			list_add(&rq->queuelist, ad->dispatch);
 			as_antic_stop(ad);
-
-		return;
+			break;
+		case ELEVATOR_INSERT_SORT:
+			BUG_ON(!blk_fs_request(rq));
+			as_add_request(ad, arq);
+			break;
+		default:
+			printk("%s: bad insert point %d\n", __FUNCTION__,where);
+			return;
 	}
 
 	if (rq_mergeable(rq)) {
 		as_add_arq_hash(ad, arq);
 
 		if (!q->last_merge)
-			q->last_merge = &rq->queuelist;
+			q->last_merge = rq;
 	}
-
-	as_add_request(ad, arq);
 }
 
 /*

@@ -1438,7 +1430,7 @@
 }
 
 static int
-as_merge(request_queue_t *q, struct list_head **insert, struct bio *bio)
+as_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
 	struct as_data *ad = q->elevator.elevator_data;
 	sector_t rb_key = bio->bi_sector + bio_sectors(bio);

@@ -1450,7 +1442,7 @@
 	 */
 	ret = elv_try_last_merge(q, bio);
 	if (ret != ELEVATOR_NO_MERGE) {
-		__rq = list_entry_rq(q->last_merge);
+		__rq = q->last_merge;
 		goto out_insert;
 	}

@@ -1482,11 +1474,11 @@
 
 	return ELEVATOR_NO_MERGE;
 out:
-	q->last_merge = &__rq->queuelist;
+	q->last_merge = __rq;
 out_insert:
 	if (ret)
 		as_hot_arq_hash(ad, RQ_DATA(__rq));
-	*insert = &__rq->queuelist;
+	*req = __rq;
 	return ret;
 }

@@ -1514,7 +1506,7 @@
 		 */
 	}
 
-	q->last_merge = &req->queuelist;
+	q->last_merge = req;
 }
 
 static void

===== drivers/block/deadline-iosched.c 1.24 vs edited =====

drivers/block/deadline-iosched.c +24 ~~-27~~

106 lines not on this page · raw message

===== drivers/block/elevator.c 1.51 vs edited =====

drivers/block/elevator.c +11 ~~-15~~

@@ -81,7 +81,7 @@
 inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
 {
 	if (q->last_merge)
-		return elv_try_merge(list_entry_rq(q->last_merge), bio);
+		return elv_try_merge(q->last_merge, bio);
 
 	return ELEVATOR_NO_MERGE;
 }

@@ -117,12 +117,12 @@
 	return 0;
 }
 
-int elv_merge(request_queue_t *q, struct list_head **entry, struct bio *bio)
+int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
 {
 	elevator_t *e = &q->elevator;
 
 	if (e->elevator_merge_fn)
-		return e->elevator_merge_fn(q, entry, bio);
+		return e->elevator_merge_fn(q, req, bio);
 
 	return ELEVATOR_NO_MERGE;
 }

@@ -140,7 +140,7 @@
 {
 	elevator_t *e = &q->elevator;
 
-	if (q->last_merge == &next->queuelist)
+	if (q->last_merge == next)
 		q->last_merge = NULL;
 
 	if (e->elevator_merge_req_fn)

@@ -156,29 +156,25 @@
 	if (q->elevator.elevator_requeue_req_fn)
 		q->elevator.elevator_requeue_req_fn(q, rq);
 	else
-		__elv_add_request(q, rq, 0, 0);
+		__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
 }
 
-void __elv_add_request(request_queue_t *q, struct request *rq, int at_end,
+void __elv_add_request(request_queue_t *q, struct request *rq, int where,
 		       int plug)
 {
-	struct list_head *insert = NULL;
-
-	if (!at_end)
-		insert = &q->queue_head;
 	if (plug)
 		blk_plug_device(q);
 
-	q->elevator.elevator_add_req_fn(q, rq, insert);
+	q->elevator.elevator_add_req_fn(q, rq, where);
 }
 
-void elv_add_request(request_queue_t *q, struct request *rq, int at_end,
+void elv_add_request(request_queue_t *q, struct request *rq, int where,
 		     int plug)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(q->queue_lock, flags);
-	__elv_add_request(q, rq, at_end, plug);
+	__elv_add_request(q, rq, where, plug);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }

@@ -200,7 +196,7 @@
 		 */
 		rq->flags |= REQ_STARTED;
 
-		if (&rq->queuelist == q->last_merge)
+		if (rq == q->last_merge)
 			q->last_merge = NULL;
 
 		if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)

@@ -238,7 +234,7 @@
 	 * deleted without ever being given to driver (merged with another
 	 * request).
 	 */
-	if (&rq->queuelist == q->last_merge)
+	if (rq == q->last_merge)
 		q->last_merge = NULL;
 
 	if (e->elevator_remove_req_fn)

===== drivers/block/ll_rw_blk.c 1.210 vs edited =====

drivers/block/ll_rw_blk.c +13 ~~-19~~

@@ -703,7 +703,7 @@
 			blk_queue_end_tag(q, rq);
 
 		rq->flags &= ~REQ_STARTED;
-		__elv_add_request(q, rq, 0, 0);
+		__elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
 	}
 }

@@ -1638,11 +1638,16 @@
 	if(reinsert) {
 		blk_requeue_request(q, rq);
 	} else {
+		int where = ELEVATOR_INSERT_BACK;
+
+		if (at_head)
+			where = ELEVATOR_INSERT_FRONT;
+
 		if (blk_rq_tagged(rq))
 			blk_queue_end_tag(q, rq);
 
 		drive_stat_acct(rq, rq->nr_sectors, 1);
-		__elv_add_request(q, rq, !at_head, 0);
+		__elv_add_request(q, rq, where, 0);
 	}
 	q->request_fn(q);
 	spin_unlock_irqrestore(q->queue_lock, flags);

@@ -1675,8 +1680,7 @@
  * queue lock is held and interrupts disabled, as we muck with the
  * request queue list.
  */
-static inline void add_request(request_queue_t * q, struct request * req,
-			       struct list_head *insert_here)
+static inline void add_request(request_queue_t * q, struct request * req)
 {
 	drive_stat_acct(req, req->nr_sectors, 1);

@@ -1687,7 +1691,7 @@
 	 * elevator indicated where it wants this request to be
 	 * inserted at elevator_merge time
 	 */
-	__elv_add_request_pos(q, req, insert_here);
+	__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
 }
  
 /*

@@ -1886,7 +1890,6 @@
 {
 	struct request *req, *freereq = NULL;
 	int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, ra;
-	struct list_head *insert_here;
 	sector_t sector;
 
 	sector = bio->bi_sector;

@@ -1909,7 +1912,6 @@
 	ra = bio->bi_rw & (1 << BIO_RW_AHEAD);
 
 again:
-	insert_here = NULL;
 	spin_lock_irq(q->queue_lock);
 
 	if (elv_queue_empty(q)) {

@@ -1919,17 +1921,13 @@
 	if (barrier)
 		goto get_rq;
 
-	el_ret = elv_merge(q, &insert_here, bio);
+	el_ret = elv_merge(q, &req, bio);
 	switch (el_ret) {
 		case ELEVATOR_BACK_MERGE:
-			req = list_entry_rq(insert_here);
-
 			BUG_ON(!rq_mergeable(req));
 
-			if (!q->back_merge_fn(q, req, bio)) {
-				insert_here = &req->queuelist;
+			if (!q->back_merge_fn(q, req, bio))
 				break;
-			}
 
 			req->biotail->bi_next = bio;
 			req->biotail = bio;

@@ -1940,14 +1938,10 @@
 			goto out;
 
 		case ELEVATOR_FRONT_MERGE:
-			req = list_entry_rq(insert_here);
-
 			BUG_ON(!rq_mergeable(req));
 
-			if (!q->front_merge_fn(q, req, bio)) {
-				insert_here = req->queuelist.prev;
+			if (!q->front_merge_fn(q, req, bio))
 				break;
-			}
 
 			bio->bi_next = req->bio;
 			req->cbio = req->bio = bio;

@@ -2035,7 +2029,7 @@
 	req->rq_disk = bio->bi_bdev->bd_disk;
 	req->start_time = jiffies;
 
-	add_request(q, req, insert_here);
+	add_request(q, req);
 out:
 	if (freereq)
 		__blk_put_request(q, freereq);

===== drivers/block/noop-iosched.c 1.1 vs edited =====

drivers/block/noop-iosched.c +11 -8

@@ -17,17 +17,15 @@
 /*
  * See if we can find a request that this buffer can be coalesced with.
  */
-int elevator_noop_merge(request_queue_t *q, struct list_head **insert,
+int elevator_noop_merge(request_queue_t *q, struct request **req,
 			struct bio *bio)
 {
 	struct list_head *entry = &q->queue_head;
 	struct request *__rq;
 	int ret;
 
-	if ((ret = elv_try_last_merge(q, bio))) {
-		*insert = q->last_merge;
+	if ((ret = elv_try_last_merge(q, bio)))
 		return ret;
-	}
 
 	while ((entry = entry->prev) != &q->queue_head) {
 		__rq = list_entry_rq(entry);

@@ -41,8 +39,8 @@
 			continue;
 
 		if ((ret = elv_try_merge(__rq, bio))) {
-			*insert = &__rq->queuelist;
-			q->last_merge = &__rq->queuelist;
+			*req = __rq;
+			q->last_merge = __rq;
 			return ret;
 		}
 	}

@@ -57,8 +55,13 @@
 }
 
 void elevator_noop_add_request(request_queue_t *q, struct request *rq,
-			       struct list_head *insert_here)
+			       int where)
 {
+	struct list_head *insert = q->queue_head.prev;
+
+	if (where == ELEVATOR_INSERT_FRONT)
+		insert = &q->queue_head;
+
 	list_add_tail(&rq->queuelist, &q->queue_head);
 
 	/*

@@ -67,7 +70,7 @@
 	if (rq->flags & REQ_HARDBARRIER)
 		q->last_merge = NULL;
 	else if (!q->last_merge)
-		q->last_merge = &rq->queuelist;
+		q->last_merge = rq;
 }
 
 struct request *elevator_noop_next_request(request_queue_t *q)

===== drivers/block/scsi_ioctl.c 1.33 vs edited =====

drivers/block/scsi_ioctl.c +1 -1

@@ -68,7 +68,7 @@
 
 	rq->flags |= REQ_NOMERGE;
 	rq->waiting = &wait;
-	elv_add_request(q, rq, 1, 1);
+	elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
 	generic_unplug_device(q);
 	wait_for_completion(&wait);

===== drivers/ide/ide-io.c 1.18 vs edited =====

drivers/ide/ide-io.c +3 -3

@@ -1387,7 +1387,7 @@
 	unsigned long flags;
 	ide_hwgroup_t *hwgroup = HWGROUP(drive);
 	DECLARE_COMPLETION(wait);
-	int insert_end = 1, err;
+	int where = ELEVATOR_INSERT_BACK, err;
 	int must_wait = (action == ide_wait || action == ide_head_wait);
 
 #ifdef CONFIG_BLK_DEV_PDC4030

@@ -1419,10 +1419,10 @@
 	spin_lock_irqsave(&ide_lock, flags);
 	if (action == ide_preempt || action == ide_head_wait) {
 		hwgroup->rq = NULL;
-		insert_end = 0;
+		where = ELEVATOR_INSERT_FRONT;
 		rq->flags |= REQ_PREEMPT;
 	}
-	__elv_add_request(drive->queue, rq, insert_end, 0);
+	__elv_add_request(drive->queue, rq, where, 0);
 	ide_do_request(hwgroup, IDE_NO_IRQ);
 	spin_unlock_irqrestore(&ide_lock, flags);

===== include/linux/blkdev.h 1.125 vs edited =====

include/linux/blkdev.h +1 -1

@@ -270,7 +270,7 @@
 	 * Together with queue_head for cacheline sharing
 	 */
 	struct list_head	queue_head;
-	struct list_head	*last_merge;
+	struct request		*last_merge;
 	elevator_t		elevator;
 
 	/*

===== include/linux/elevator.h 1.28 vs edited =====

include/linux/elevator.h +10 -6

@@ -1,7 +1,7 @@
 #ifndef _LINUX_ELEVATOR_H
 #define _LINUX_ELEVATOR_H
 
-typedef int (elevator_merge_fn) (request_queue_t *, struct list_head **,
+typedef int (elevator_merge_fn) (request_queue_t *, struct request **,
 				 struct bio *);
 
 typedef void (elevator_merge_req_fn) (request_queue_t *, struct request *, struct request *);

@@ -10,7 +10,7 @@
 
 typedef struct request *(elevator_next_req_fn) (request_queue_t *);
 
-typedef void (elevator_add_req_fn) (request_queue_t *, struct request *, struct list_head *);
+typedef void (elevator_add_req_fn) (request_queue_t *, struct request *, int);
 typedef int (elevator_queue_empty_fn) (request_queue_t *);
 typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
 typedef void (elevator_requeue_req_fn) (request_queue_t *, struct request *);

@@ -62,7 +62,7 @@
  */
 extern void elv_add_request(request_queue_t *, struct request *, int, int);
 extern void __elv_add_request(request_queue_t *, struct request *, int, int);
-extern int elv_merge(request_queue_t *, struct list_head **, struct bio *);
+extern int elv_merge(request_queue_t *, struct request **, struct bio *);
 extern void elv_merge_requests(request_queue_t *, struct request *,
 			       struct request *);
 extern void elv_merged_request(request_queue_t *, struct request *);

@@ -79,9 +79,6 @@
 extern int elv_set_request(request_queue_t *, struct request *, int);
 extern void elv_put_request(request_queue_t *, struct request *);
 
-#define __elv_add_request_pos(q, rq, pos)	\
-	(q)->elevator.elevator_add_req_fn((q), (rq), (pos))
-
 /*
  * noop I/O scheduler. always merges, always inserts new request at tail
  */

@@ -115,5 +112,12 @@
 #define ELEVATOR_NO_MERGE	0
 #define ELEVATOR_FRONT_MERGE	1
 #define ELEVATOR_BACK_MERGE	2
+
+/*
+ * Insertion selection
+ */
+#define ELEVATOR_INSERT_FRONT	1
+#define ELEVATOR_INSERT_BACK	2
+#define ELEVATOR_INSERT_SORT	3
 
 #endif

Signature · 1 line

Jens Axboe

Martin Schlemmer

2003-09-05 22:01 UTC #5 lore raw

Quoted 12 lines · Jens Axboe

Quoted 10 lines · Jens Axboe
Quoted 8 lines
Jens, if insert_here is dead, there is no point to passing back a hint because it can't get back to the elevator anyway.
I'd very much like to kill insert_here and be done with it. If another io scheduler comes along with a good use for it then the writers can come up with an elegant solution ;) Hey, if they know a NO_MERGE return means an insert will soon happen under the same lock, they could keep it cached privately.
Agree, lets just kill it off.

Quoted 9 lines

Here's the patch that kills it and its associated logic off completely. Nick, I'm not too sure what the logic was for stopping anticipation in as_insert_request() (the insert_here tests were somewhat convoluted :), I've added what I think makes most sense: stop anticipating if someone puts a request at the head of the dispatch list.
It also makes the *_insert_request strategies much easier to follow, imo.

Hmm, do not know if its just me, but I just got two processes (cp's) in D state. They did complete though, but throughput was not good. Any tips on getting it debugged ?

Thanks,

Signature · 1 line

Martin Schlemmer

Nick Piggin

author

2003-09-06 01:34 UTC #6 lore raw

Quoted 21 lines · Martin Schlemmer

Quoted 19 lines · Jens Axboe
Quoted 11 lines · Jens Axboe
Quoted 9 lines
Jens, if insert_here is dead, there is no point to passing back a hint because it can't get back to the elevator anyway.
I'd very much like to kill insert_here and be done with it. If another io scheduler comes along with a good use for it then the writers can come up with an elegant solution ;) Hey, if they know a NO_MERGE return means an insert will soon happen under the same lock, they could keep it cached privately.
Agree, lets just kill it off.
Here's the patch that kills it and its associated logic off completely. Nick, I'm not too sure what the logic was for stopping anticipation in as_insert_request() (the insert_here tests were somewhat convoluted :), I've added what I think makes most sense: stop anticipating if someone puts a request at the head of the dispatch list.

Quoted 9 lines

Quoted 4 lines
It also makes the *_insert_request strategies much easier to follow, imo.
Hmm, do not know if its just me, but I just got two processes (cp's) in D state. They did complete though, but throughput was not good. Any tips on getting it debugged ?

If they complete at all, then its very unlikely for them to be slowed down (AS can do this a bit though). If you could get a comparison with my patch that started the problems backed out it might tell me something. Thanks.