This patch changes the dm path selector interface for dynamic
load balancers:
o adding a new hook, start_io()
o adding 'nr_bytes' parameter 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 used by path selectors for
size-based decision.
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>
Cc: Vijayakumar Balasubramanian <vijayakumar@hp.com>
Cc: Alasdair G Kergon <agk@redhat.com>
---
drivers/md/dm-mpath.c | 28 ++++++++++++++++++----------
drivers/md/dm-path-selector.h | 8 ++++++--
drivers/md/dm-round-robin.c | 2 +-
3 files changed, 25 insertions(+), 13 deletions(-)

Index: 2.6.29-rc8/drivers/md/dm-mpath.c
================================================== =================
--- 2.6.29-rc8.orig/drivers/md/dm-mpath.c
+++ 2.6.29-rc8/drivers/md/dm-mpath.c
@@ -103,6 +103,7 @@ 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);
@@ -251,11 +252,12 @@ static void __switch_pg(struct multipath
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;

@@ -267,7 +269,7 @@ static int __choose_path_in_pg(struct mu
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;
@@ -279,12 +281,12 @@ static void __choose_pgpath(struct multi
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;

/*
@@ -296,7 +298,7 @@ static void __choose_pgpath(struct multi
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--);
@@ -327,6 +329,7 @@ static int map_io(struct multipath *m, s
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;

@@ -335,7 +338,7 @@ static int map_io(struct multipath *m, s
/* 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;

@@ -360,6 +363,11 @@ static int map_io(struct multipath *m, s
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);

@@ -438,7 +446,7 @@ static void process_queued_ios(struct wo
goto out;

if (!m->current_pgpath)
- __choose_pgpath(m);
+ __choose_pgpath(m, 0);

pgpath = m->current_pgpath;

@@ -1196,7 +1204,7 @@ static int multipath_end_io(struct dm_ta
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);
@@ -1412,7 +1420,7 @@ static int multipath_ioctl(struct dm_tar
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;
Index: 2.6.29-rc8/drivers/md/dm-path-selector.h
================================================== =================
--- 2.6.29-rc8.orig/drivers/md/dm-path-selector.h
+++ 2.6.29-rc8/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 */
Index: 2.6.29-rc8/drivers/md/dm-round-robin.c
================================================== =================
--- 2.6.29-rc8.orig/drivers/md/dm-round-robin.c
+++ 2.6.29-rc8/drivers/md/dm-round-robin.c
@@ -161,7 +161,7 @@ static int rr_reinstate_path(struct path
}

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;

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