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Commit 15853af9 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

[BLOCK] Implement elv_drain_elevator for improved switch error detection 



This patch adds request_queue->nr_sorted which keeps the number of
requests in the iosched and implement elv_drain_elevator which
performs forced dispatching.  elv_drain_elevator checks whether
iosched actually dispatches all requests it has and prints error
message if it doesn't.  As buggy forced dispatching can result in
wrong barrier operations, I think this extra check is worthwhile.

Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
Signed-off-by: default avatarJens Axboe <axboe@suse.de>
parent 1b5ed5e1

block/elevator.c

+20 −5
Original line number Diff line number Diff line
@@ -226,6 +226,7 @@ void elv_dispatch_sort(request_queue_t *q, struct request *rq) 


	if (q->last_merge == rq)

		q->last_merge = NULL;

	q->nr_sorted--;



	boundary = q->end_sector;
@@ -284,6 +285,7 @@ void elv_merge_requests(request_queue_t *q, struct request *rq, 


	if (e->ops->elevator_merge_req_fn)

		e->ops->elevator_merge_req_fn(q, rq, next);

	q->nr_sorted--;



	q->last_merge = rq;

}
@@ -315,6 +317,20 @@ void elv_requeue_request(request_queue_t *q, struct request *rq) 
	__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);

}



static void elv_drain_elevator(request_queue_t *q)

{

	static int printed;

	while (q->elevator->ops->elevator_dispatch_fn(q, 1))

		;

	if (q->nr_sorted == 0)

		return;

	if (printed++ < 10) {

		printk(KERN_ERR "%s: forced dispatching is broken "

		       "(nr_sorted=%u), please report this\n",

		       q->elevator->elevator_type->elevator_name, q->nr_sorted);

	}

}



void __elv_add_request(request_queue_t *q, struct request *rq, int where,

		       int plug)

{
@@ -349,9 +365,7 @@ void __elv_add_request(request_queue_t *q, struct request *rq, int where, 


	case ELEVATOR_INSERT_BACK:

		rq->flags |= REQ_SOFTBARRIER;



		while (q->elevator->ops->elevator_dispatch_fn(q, 1))

			;

		elv_drain_elevator(q);

		list_add_tail(&rq->queuelist, &q->queue_head);

		/*

		 * We kick the queue here for the following reasons.
@@ -370,6 +384,7 @@ void __elv_add_request(request_queue_t *q, struct request *rq, int where, 
	case ELEVATOR_INSERT_SORT:

		BUG_ON(!blk_fs_request(rq));

		rq->flags |= REQ_SORTED;

		q->nr_sorted++;

		if (q->last_merge == NULL && rq_mergeable(rq))

			q->last_merge = rq;

		/*
@@ -692,8 +707,7 @@ static void elevator_switch(request_queue_t *q, struct elevator_type *new_e) 


	set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);



	while (q->elevator->ops->elevator_dispatch_fn(q, 1))

		;

	elv_drain_elevator(q);



	while (q->rq.elvpriv) {

		blk_remove_plug(q);
@@ -701,6 +715,7 @@ static void elevator_switch(request_queue_t *q, struct elevator_type *new_e) 
		spin_unlock_irq(q->queue_lock);

		msleep(10);

		spin_lock_irq(q->queue_lock);

		elv_drain_elevator(q);

	}



	spin_unlock_irq(q->queue_lock);

include/linux/blkdev.h

+2 −0
Original line number Diff line number Diff line
@@ -406,6 +406,7 @@ struct request_queue 


	atomic_t		refcnt;



	unsigned int		nr_sorted;

	unsigned int		in_flight;



	/*
@@ -631,6 +632,7 @@ static inline void elv_dispatch_add_tail(struct request_queue *q, 
{

	if (q->last_merge == rq)

		q->last_merge = NULL;

	q->nr_sorted--;



	q->end_sector = rq_end_sector(rq);

	q->boundary_rq = rq;