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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: Mike Snitzer <snitzer@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
hifive-unleashed-5.1
Mike Snitzer 2016-09-09 19:26:19 -04:00
parent 7e48c768f4
commit b88efd43f9
1 changed files with 9 additions and 6 deletions
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15
drivers/md/dm-mpath.c
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@ -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);