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 <snit...@redhat.com>
---
drivers/md/dm-mpath.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index f69715b..f31fa13 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -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);
--
2.7.4 (Apple Git-66)
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