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>

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index f1cf8f7..890c0e8 100644 (file)
--- 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 27357b8..e7d1fa8 100644 (file)
--- 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 cdfbf65..24752f4 100644 (file)
--- 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;