[PATCH 1/2] block: elevator quiescing helpers

[PATCH 1/2] block: elevator quiescing helpers

[Jerome Marchand]

From: Jens Axboe <jens.axboe@oracle.com>

Simple helper functions to quiesce the request queue.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
---
 block/blk.h      |    4 ++++
 block/elevator.c |   40 +++++++++++++++++++++++++++-------------
 2 files changed, 31 insertions(+), 13 deletions(-)

Index: linux-2.6/block/blk.h
===================================================================
--- linux-2.6.orig/block/blk.h
+++ linux-2.6/block/blk.h
@@ -70,6 +70,10 @@ void blk_queue_congestion_threshold(stru

 int blk_dev_init(void);

+void elv_quisce_start(struct request_queue *q);
+void elv_quisce_end(struct request_queue *q);
+
+
 /*
  * Return the threshold (number of used requests) at which the queue is
  * considered to be congested.  It include a little hysteresis to keep the
Index: linux-2.6/block/elevator.c
===================================================================
--- linux-2.6.orig/block/elevator.c
+++ linux-2.6/block/elevator.c
@@ -587,6 +587,31 @@ static void elv_drain_elevator(struct re
 	}
 }

+/*
+ * Call with queue lock held, interrupts disabled
+ */
+void elv_quisce_start(struct request_queue *q)
+{
+	queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
+
+	/*
+	 * make sure we don't have any requests in flight
+	 */
+	elv_drain_elevator(q);
+	while (q->rq.elvpriv) {
+		blk_start_queueing(q);
+		spin_unlock_irq(q->queue_lock);
+		msleep(10);
+		spin_lock_irq(q->queue_lock);
+		elv_drain_elevator(q);
+	}
+}
+
+void elv_quisce_end(struct request_queue *q)
+{
+	queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+}
+
 void elv_insert(struct request_queue *q, struct request *rq, int where)
 {
 	struct list_head *pos;
@@ -1101,18 +1126,7 @@ static int elevator_switch(struct reques
 	 * Turn on BYPASS and drain all requests w/ elevator private data
 	 */
 	spin_lock_irq(q->queue_lock);
-
-	queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
-
-	elv_drain_elevator(q);
-
-	while (q->rq.elvpriv) {
-		blk_start_queueing(q);
-		spin_unlock_irq(q->queue_lock);
-		msleep(10);
-		spin_lock_irq(q->queue_lock);
-		elv_drain_elevator(q);
-	}
+	elv_quisce_start(q);

 	/*
 	 * Remember old elevator.
@@ -1136,7 +1150,7 @@ static int elevator_switch(struct reques
 	 */
 	elevator_exit(old_elevator);
 	spin_lock_irq(q->queue_lock);
-	queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+	elv_quisce_end(q);
 	spin_unlock_irq(q->queue_lock);

 	blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);

[PATCH 2/2] block: fix inconsistency in I/O stat accounting code

[Jerome Marchand]

This forces in_flight to be zero when turning off or on the I/O stat
accounting and stops updating I/O stats in attempt_merge() when
accounting is turned off.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
---
 block/blk-core.c         |   13 ++++---------
 block/blk-merge.c        |   29 +++++++++++++++++------------
 block/blk-sysfs.c        |    4 ++++
 block/blk.h              |   10 ++++++----
 block/elevator.c         |    2 +-
 include/linux/elevator.h |    1 +
 6 files changed, 33 insertions(+), 26 deletions(-)

Index: linux-2.6/block/blk-core.c
===================================================================
--- linux-2.6.orig/block/blk-core.c
+++ linux-2.6/block/blk-core.c
@@ -64,12 +64,11 @@ static struct workqueue_struct *kblockd_

 static void drive_stat_acct(struct request *rq, int new_io)
 {
-	struct gendisk *disk = rq->rq_disk;
 	struct hd_struct *part;
 	int rw = rq_data_dir(rq);
 	int cpu;

-	if (!blk_fs_request(rq) || !disk || !blk_do_io_stat(disk->queue))
+	if (!blk_fs_request(rq) || !blk_do_io_stat(rq))
 		return;

 	cpu = part_stat_lock();
@@ -1665,9 +1664,7 @@ EXPORT_SYMBOL(blkdev_dequeue_request);

 static void blk_account_io_completion(struct request *req, unsigned int
bytes)
 {
-	struct gendisk *disk = req->rq_disk;
-
-	if (!disk || !blk_do_io_stat(disk->queue))
+	if (!blk_do_io_stat(req))
 		return;

 	if (blk_fs_request(req)) {
@@ -1684,9 +1681,7 @@ static void blk_account_io_completion(st

 static void blk_account_io_done(struct request *req)
 {
-	struct gendisk *disk = req->rq_disk;
-
-	if (!disk || !blk_do_io_stat(disk->queue))
+	if (!blk_do_io_stat(req))
 		return;

 	/*
@@ -1701,7 +1696,7 @@ static void blk_account_io_done(struct r
 		int cpu;

 		cpu = part_stat_lock();
-		part = disk_map_sector_rcu(disk, req->sector);
+		part = disk_map_sector_rcu(req->rq_disk, req->sector);

 		part_stat_inc(cpu, part, ios[rw]);
 		part_stat_add(cpu, part, ticks[rw], duration);
Index: linux-2.6/block/blk-merge.c
===================================================================
--- linux-2.6.orig/block/blk-merge.c
+++ linux-2.6/block/blk-merge.c
@@ -338,6 +338,22 @@ static int ll_merge_requests_fn(struct r
 	return 1;
 }

+static void blk_account_io_merge(struct request *req)
+{
+	if (blk_do_io_stat(req)) {
+		struct hd_struct *part;
+		int cpu;
+
+		cpu = part_stat_lock();
+		part = disk_map_sector_rcu(req->rq_disk, req->sector);
+
+		part_round_stats(cpu, part);
+		part_dec_in_flight(part);
+
+		part_stat_unlock();
+	}
+}
+
 /*
  * Has to be called with the request spinlock acquired
  */
@@ -386,18 +402,7 @@ static int attempt_merge(struct request_

 	elv_merge_requests(q, req, next);

-	if (req->rq_disk) {
-		struct hd_struct *part;
-		int cpu;
-
-		cpu = part_stat_lock();
-		part = disk_map_sector_rcu(req->rq_disk, req->sector);
-
-		part_round_stats(cpu, part);
-		part_dec_in_flight(part);
-
-		part_stat_unlock();
-	}
+	blk_account_io_merge(req);

 	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
 	if (blk_rq_cpu_valid(next))
Index: linux-2.6/block/blk-sysfs.c
===================================================================
--- linux-2.6.orig/block/blk-sysfs.c
+++ linux-2.6/block/blk-sysfs.c
@@ -209,10 +209,14 @@ static ssize_t queue_iostats_store(struc
 	ssize_t ret = queue_var_store(&stats, page, count);

 	spin_lock_irq(q->queue_lock);
+	elv_quisce_start(q);
+
 	if (stats)
 		queue_flag_set(QUEUE_FLAG_IO_STAT, q);
 	else
 		queue_flag_clear(QUEUE_FLAG_IO_STAT, q);
+
+	elv_quisce_end(q);
 	spin_unlock_irq(q->queue_lock);

 	return ret;
Index: linux-2.6/block/blk.h
===================================================================
--- linux-2.6.orig/block/blk.h
+++ linux-2.6/block/blk.h
@@ -112,12 +112,14 @@ static inline int blk_cpu_to_group(int c
 #endif
 }

-static inline int blk_do_io_stat(struct request_queue *q)
+static inline int blk_do_io_stat(struct request *rq)
 {
-	if (q)
-		return blk_queue_io_stat(q);
+	struct gendisk *disk = rq->rq_disk;

-	return 0;
+	if (!disk || !disk->queue)
+		return 0;
+
+	return blk_queue_io_stat(disk->queue) && (rq->cmd_flags & REQ_ELVPRIV);
 }

 #endif
Index: linux-2.6/block/elevator.c
===================================================================
--- linux-2.6.orig/block/elevator.c
+++ linux-2.6/block/elevator.c
@@ -573,7 +573,7 @@ void elv_requeue_request(struct request_
 	elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
 }

-static void elv_drain_elevator(struct request_queue *q)
+void elv_drain_elevator(struct request_queue *q)
 {
 	static int printed;
 	while (q->elevator->ops->elevator_dispatch_fn(q, 1))
Index: linux-2.6/include/linux/elevator.h
===================================================================
--- linux-2.6.orig/include/linux/elevator.h
+++ linux-2.6/include/linux/elevator.h
@@ -116,6 +116,7 @@ extern void elv_abort_queue(struct reque
 extern void elv_completed_request(struct request_queue *, struct
request *);
 extern int elv_set_request(struct request_queue *, struct request *,
gfp_t);
 extern void elv_put_request(struct request_queue *, struct request *);
+extern void elv_drain_elevator(struct request_queue *);

 /*
  * io scheduler registration

Re: [PATCH 2/2] block: fix inconsistency in I/O stat accounting code

[Jens Axboe]

On Thu, Mar 26 2009, Jerome Marchand wrote:
> This forces in_flight to be zero when turning off or on the I/O stat
> accounting and stops updating I/O stats in attempt_merge() when
> accounting is turned off.

Good stuff, thanks for doing this Jerome! I'll test it and queue it up
for 2.6.30. Then we can later do a -stable backport as well, if things
work out.

-- 
Jens Axboe