Commit b88efd43 authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm mpath: delay the requeue of blk-mq requests while all paths down 



Return DM_MAPIO_DELAY_REQUEUE from .clone_and_map_rq.  Also, return
false from .busy, if all paths are down, so that blk-mq requests get
mapped via .clone_and_map_rq -- which results in DM_MAPIO_DELAY_REQUEUE
being returned to dm-rq.

This change allows for a noticeable reduction in cpu utilization
(reduced kworker load) while all paths are down, e.g.:

system CPU idleness (as measured by fio's --idle-prof=system):
before: system: 86.58%
after:  system: 98.60%

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
parent 7e48c768

drivers/md/dm-mpath.c

+9 −6
Original line number Diff line number Diff line
@@ -550,9 +550,9 @@ static int __multipath_map(struct dm_target *ti, struct request *clone, 
		pgpath = choose_pgpath(m, nr_bytes);



	if (!pgpath) {

		if (!must_push_back_rq(m))

			r = -EIO;	/* Failed */

		return r;

		if (must_push_back_rq(m))

			return DM_MAPIO_DELAY_REQUEUE;

		return -EIO;	/* Failed */

	} else if (test_bit(MPATHF_QUEUE_IO, &m->flags) ||

		   test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) {

		pg_init_all_paths(m);
@@ -1992,11 +1992,14 @@ static int multipath_busy(struct dm_target *ti) 
	struct priority_group *pg, *next_pg;

	struct pgpath *pgpath;



	/* pg_init in progress or no paths available */

	if (atomic_read(&m->pg_init_in_progress) ||

	    (!atomic_read(&m->nr_valid_paths) && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)))

	/* pg_init in progress */

	if (atomic_read(&m->pg_init_in_progress))

		return true;



	/* no paths available, for blk-mq: rely on IO mapping to delay requeue */

	if (!atomic_read(&m->nr_valid_paths) && test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))

		return (m->queue_mode != DM_TYPE_MQ_REQUEST_BASED);



	/* Guess which priority_group will be used at next mapping time */

	pg = lockless_dereference(m->current_pg);

	next_pg = lockless_dereference(m->next_pg);

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