Commit 86ff7c2a authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: introduce BLK_STS_DEV_RESOURCE 



This status is returned from driver to block layer if device related
resource is unavailable, but driver can guarantee that IO dispatch
will be triggered in future when the resource is available.

Convert some drivers to return BLK_STS_DEV_RESOURCE.  Also, if driver
returns BLK_STS_RESOURCE and SCHED_RESTART is set, rerun queue after
a delay (BLK_MQ_DELAY_QUEUE) to avoid IO stalls.  BLK_MQ_DELAY_QUEUE is
3 ms because both scsi-mq and nvmefc are using that magic value.

If a driver can make sure there is in-flight IO, it is safe to return
BLK_STS_DEV_RESOURCE because:

1) If all in-flight IOs complete before examining SCHED_RESTART in
blk_mq_dispatch_rq_list(), SCHED_RESTART must be cleared, so queue
is run immediately in this case by blk_mq_dispatch_rq_list();

2) if there is any in-flight IO after/when examining SCHED_RESTART
in blk_mq_dispatch_rq_list():
- if SCHED_RESTART isn't set, queue is run immediately as handled in 1)
- otherwise, this request will be dispatched after any in-flight IO is
  completed via blk_mq_sched_restart()

3) if SCHED_RESTART is set concurently in context because of
BLK_STS_RESOURCE, blk_mq_delay_run_hw_queue() will cover the above two
cases and make sure IO hang can be avoided.

One invariant is that queue will be rerun if SCHED_RESTART is set.

Suggested-by: default avatarJens Axboe <axboe@kernel.dk>
Tested-by: default avatarLaurence Oberman <loberman@redhat.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 0a4b6e2f

block/blk-core.c

+1 −0
Original line number Diff line number Diff line
@@ -145,6 +145,7 @@ static const struct { 
	[BLK_STS_MEDIUM]	= { -ENODATA,	"critical medium" },

	[BLK_STS_PROTECTION]	= { -EILSEQ,	"protection" },

	[BLK_STS_RESOURCE]	= { -ENOMEM,	"kernel resource" },

	[BLK_STS_DEV_RESOURCE]	= { -EBUSY,	"device resource" },

	[BLK_STS_AGAIN]		= { -EAGAIN,	"nonblocking retry" },



	/* device mapper special case, should not leak out: */

block/blk-mq.c

+16 −4
Original line number Diff line number Diff line
@@ -1162,6 +1162,8 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx **hctx, 
	return true;

}



#define BLK_MQ_RESOURCE_DELAY	3		/* ms units */



bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,

			     bool got_budget)

{
@@ -1169,6 +1171,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, 
	struct request *rq, *nxt;

	bool no_tag = false;

	int errors, queued;

	blk_status_t ret = BLK_STS_OK;



	if (list_empty(list))

		return false;
@@ -1181,7 +1184,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, 
	errors = queued = 0;

	do {

		struct blk_mq_queue_data bd;

		blk_status_t ret;



		rq = list_first_entry(list, struct request, queuelist);

		if (!blk_mq_get_driver_tag(rq, &hctx, false)) {
@@ -1226,7 +1228,7 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, 
		}



		ret = q->mq_ops->queue_rq(hctx, &bd);

		if (ret == BLK_STS_RESOURCE) {

		if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {

			/*

			 * If an I/O scheduler has been configured and we got a

			 * driver tag for the next request already, free it
@@ -1257,6 +1259,8 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, 
	 * that is where we will continue on next queue run.

	 */

	if (!list_empty(list)) {

		bool needs_restart;



		spin_lock(&hctx->lock);

		list_splice_init(list, &hctx->dispatch);

		spin_unlock(&hctx->lock);
@@ -1280,10 +1284,17 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list, 
		 * - Some but not all block drivers stop a queue before

		 *   returning BLK_STS_RESOURCE. Two exceptions are scsi-mq

		 *   and dm-rq.

		 *

		 * If driver returns BLK_STS_RESOURCE and SCHED_RESTART

		 * bit is set, run queue after a delay to avoid IO stalls

		 * that could otherwise occur if the queue is idle.

		 */

		if (!blk_mq_sched_needs_restart(hctx) ||

		needs_restart = blk_mq_sched_needs_restart(hctx);

		if (!needs_restart ||

		    (no_tag && list_empty_careful(&hctx->dispatch_wait.entry)))

			blk_mq_run_hw_queue(hctx, true);

		else if (needs_restart && (ret == BLK_STS_RESOURCE))

			blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);

	}



	return (queued + errors) != 0;
@@ -1764,6 +1775,7 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx, 
		*cookie = new_cookie;

		break;

	case BLK_STS_RESOURCE:

	case BLK_STS_DEV_RESOURCE:

		__blk_mq_requeue_request(rq);

		break;

	default:
@@ -1826,7 +1838,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, 
	hctx_lock(hctx, &srcu_idx);



	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false);

	if (ret == BLK_STS_RESOURCE)

	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)

		blk_mq_sched_insert_request(rq, false, true, false);

	else if (ret != BLK_STS_OK)

		blk_mq_end_request(rq, ret);

drivers/block/null_blk.c

+1 −1
Original line number Diff line number Diff line
@@ -1230,7 +1230,7 @@ static blk_status_t null_handle_cmd(struct nullb_cmd *cmd) 
				return BLK_STS_OK;

			} else

				/* requeue request */

				return BLK_STS_RESOURCE;

				return BLK_STS_DEV_RESOURCE;

		}

	}

drivers/block/virtio_blk.c

+1 −1
Original line number Diff line number Diff line
@@ -276,7 +276,7 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, 
		/* Out of mem doesn't actually happen, since we fall back

		 * to direct descriptors */

		if (err == -ENOMEM || err == -ENOSPC)

			return BLK_STS_RESOURCE;

			return BLK_STS_DEV_RESOURCE;

		return BLK_STS_IOERR;

	}

drivers/block/xen-blkfront.c

+1 −1
Original line number Diff line number Diff line
@@ -911,7 +911,7 @@ out_err: 
out_busy:

	blk_mq_stop_hw_queue(hctx);

	spin_unlock_irqrestore(&rinfo->ring_lock, flags);

	return BLK_STS_RESOURCE;

	return BLK_STS_DEV_RESOURCE;

}



static void blkif_complete_rq(struct request *rq)

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