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Commit 02ab823f authored by Kiyoshi Ueda's avatar Kiyoshi Ueda Committed by Alasdair G Kergon
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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: default avatarStefan Bader <stefan.bader@canonical.com>
Signed-off-by: default avatarKiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: default avatarJun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 2bd02345

drivers/md/dm-mpath.c

+18 −10
Original line number Diff line number Diff line
@@ -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;

drivers/md/dm-path-selector.h

+6 −2
Original line number Diff line number Diff line
@@ -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 */

drivers/md/dm-round-robin.c

+1 −1
Original line number Diff line number Diff line
@@ -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;