dm mpath: add start_io and nr_bytes to path selectors

This patch makes two additions to the dm path selector interface for
dynamic load balancers:
  o a new hook, start_io()
  o a new parameter 'nr_bytes' to select_path()/start_io()/end_io()
    to pass the size of the I/O

start_io() is called when a target driver actually submits I/O
to the selected path.
Path selectors can use it to start accounting of the I/O.
(e.g. counting the number of in-flight I/Os.)
The start_io hook is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html

nr_bytes, the size of the I/O, is so path selectors can take the
size of the I/O into account when deciding which path to use.
dm-service-time uses it to estimate service time, for example.
(Added the nr_bytes member to dm_mpath_io instead of using existing
 details.bi_size, since request-based dm patch deletes it.)

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

3 files changed, 25 insertions, 13 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index f1cf8f7449d6..890c0e8ed13e 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -101,6 +101,7 @@ struct multipath {
 struct dm_mpath_io {
         struct pgpath *pgpath;
         struct dm_bio_details details;
+        size_t nr_bytes;
 };
 
 typedef int (*action_fn) (struct pgpath *pgpath);
@@ -244,11 +245,12 @@ static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
         m->pg_init_count = 0;
 }
 
-static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg)
+static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg,
+                               size_t nr_bytes)
 {
         struct dm_path *path;
 
-        path = pg->ps.type->select_path(&pg->ps, &m->repeat_count);
+        path = pg->ps.type->select_path(&pg->ps, &m->repeat_count, nr_bytes);
         if (!path)
                 return -ENXIO;
 
@@ -260,7 +262,7 @@ static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg)
         return 0;
 }
 
-static void __choose_pgpath(struct multipath *m)
+static void __choose_pgpath(struct multipath *m, size_t nr_bytes)
 {
         struct priority_group *pg;
         unsigned bypassed = 1;
@@ -272,12 +274,12 @@ static void __choose_pgpath(struct multipath *m)
         if (m->next_pg) {
                 pg = m->next_pg;
                 m->next_pg = NULL;
-                if (!__choose_path_in_pg(m, pg))
+                if (!__choose_path_in_pg(m, pg, nr_bytes))
                         return;
         }
 
         /* Don't change PG until it has no remaining paths */
-        if (m->current_pg && !__choose_path_in_pg(m, m->current_pg))
+        if (m->current_pg && !__choose_path_in_pg(m, m->current_pg, nr_bytes))
                 return;
 
         /*
@@ -289,7 +291,7 @@ static void __choose_pgpath(struct multipath *m)
                 list_for_each_entry(pg, &m->priority_groups, list) {
                         if (pg->bypassed == bypassed)
                                 continue;
-                        if (!__choose_path_in_pg(m, pg))
+                        if (!__choose_path_in_pg(m, pg, nr_bytes))
                                 return;
                 }
         } while (bypassed--);
@@ -320,6 +322,7 @@ static int map_io(struct multipath *m, struct bio *bio,
                   struct dm_mpath_io *mpio, unsigned was_queued)
 {
         int r = DM_MAPIO_REMAPPED;
+        size_t nr_bytes = bio->bi_size;
         unsigned long flags;
         struct pgpath *pgpath;
 
@@ -328,7 +331,7 @@ static int map_io(struct multipath *m, struct bio *bio,
         /* Do we need to select a new pgpath? */
         if (!m->current_pgpath ||
             (!m->queue_io && (m->repeat_count && --m->repeat_count == 0)))
-                __choose_pgpath(m);
+                __choose_pgpath(m, nr_bytes);
 
         pgpath = m->current_pgpath;
 
@@ -353,6 +356,11 @@ static int map_io(struct multipath *m, struct bio *bio,
                 r = -EIO;       /* Failed */
 
         mpio->pgpath = pgpath;
+        mpio->nr_bytes = nr_bytes;
+
+        if (r == DM_MAPIO_REMAPPED && pgpath->pg->ps.type->start_io)
+                pgpath->pg->ps.type->start_io(&pgpath->pg->ps, &pgpath->path,
+                                              nr_bytes);
 
         spin_unlock_irqrestore(&m->lock, flags);
 
@@ -431,7 +439,7 @@ static void process_queued_ios(struct work_struct *work)
                 goto out;
 
         if (!m->current_pgpath)
-                __choose_pgpath(m);
+                __choose_pgpath(m, 0);
 
         pgpath = m->current_pgpath;
 
@@ -1209,7 +1217,7 @@ static int multipath_end_io(struct dm_target *ti, struct bio *bio,
         if (pgpath) {
                 ps = &pgpath->pg->ps;
                 if (ps->type->end_io)
-                        ps->type->end_io(ps, &pgpath->path);
+                        ps->type->end_io(ps, &pgpath->path, mpio->nr_bytes);
         }
         if (r != DM_ENDIO_INCOMPLETE)
                 mempool_free(mpio, m->mpio_pool);
@@ -1425,7 +1433,7 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
         spin_lock_irqsave(&m->lock, flags);
 
         if (!m->current_pgpath)
-                __choose_pgpath(m);
+                __choose_pgpath(m, 0);
 
         if (m->current_pgpath) {
                 bdev = m->current_pgpath->path.dev->bdev;
diff --git a/drivers/md/dm-path-selector.h b/drivers/md/dm-path-selector.h
index 27357b85d73d..e7d1fa8b0459 100644
--- a/drivers/md/dm-path-selector.h
+++ b/drivers/md/dm-path-selector.h
@@ -56,7 +56,8 @@ struct path_selector_type {
          * the path fails.
          */
         struct dm_path *(*select_path) (struct path_selector *ps,
-                                     unsigned *repeat_count);
+                                        unsigned *repeat_count,
+                                        size_t nr_bytes);
 
         /*
          * Notify the selector that a path has failed.
@@ -75,7 +76,10 @@ struct path_selector_type {
         int (*status) (struct path_selector *ps, struct dm_path *path,
                        status_type_t type, char *result, unsigned int maxlen);
 
-        int (*end_io) (struct path_selector *ps, struct dm_path *path);
+        int (*start_io) (struct path_selector *ps, struct dm_path *path,
+                         size_t nr_bytes);
+        int (*end_io) (struct path_selector *ps, struct dm_path *path,
+                       size_t nr_bytes);
 };
 
 /* Register a path selector */
diff --git a/drivers/md/dm-round-robin.c b/drivers/md/dm-round-robin.c
index cdfbf65b28cb..24752f449bef 100644
--- a/drivers/md/dm-round-robin.c
+++ b/drivers/md/dm-round-robin.c
@@ -161,7 +161,7 @@ static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
 }
 
 static struct dm_path *rr_select_path(struct path_selector *ps,
-                                   unsigned *repeat_count)
+                                      unsigned *repeat_count, size_t nr_bytes)
 {
         struct selector *s = (struct selector *) ps->context;
         struct path_info *pi = NULL;