[dm-devel] [PATCH] dm: shortcut the calls to linear_map and stripe_map

[Mikulas Patocka]

Shortcut the calls to linear_map and stripe_map, so that they don't suffer 
the overhead of retpolines used for indirect calls.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

---
 drivers/md/dm-linear.c |    2 +-
 drivers/md/dm-stripe.c |    2 +-
 drivers/md/dm.c        |   11 +++++++++--
 drivers/md/dm.h        |    2 ++
 4 files changed, 13 insertions(+), 4 deletions(-)

Index: linux-2.6/drivers/md/dm-linear.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-linear.c
+++ linux-2.6/drivers/md/dm-linear.c
@@ -85,7 +85,7 @@ static sector_t linear_map_sector(struct
 	return lc->start + dm_target_offset(ti, bi_sector);
 }
 
-static int linear_map(struct dm_target *ti, struct bio *bio)
+int linear_map(struct dm_target *ti, struct bio *bio)
 {
 	struct linear_c *lc = ti->private;
 
Index: linux-2.6/drivers/md/dm-stripe.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-stripe.c
+++ linux-2.6/drivers/md/dm-stripe.c
@@ -268,7 +268,7 @@ static int stripe_map_range(struct strip
 	return DM_MAPIO_SUBMITTED;
 }
 
-static int stripe_map(struct dm_target *ti, struct bio *bio)
+int stripe_map(struct dm_target *ti, struct bio *bio)
 {
 	struct stripe_c *sc = ti->private;
 	uint32_t stripe;
Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c
+++ linux-2.6/drivers/md/dm.c
@@ -1424,9 +1424,16 @@ static void __map_bio(struct bio *clone)
 		if (unlikely(dm_emulate_zone_append(md)))
 			r = dm_zone_map_bio(tio);
 		else
+			goto do_map;
+	} else {
+do_map:
+		if (likely(ti->type->map == linear_map))
+			r = linear_map(ti, clone);
+		else if (ti->type->map == stripe_map)
+			r = stripe_map(ti, clone);
+		else
 			r = ti->type->map(ti, clone);
-	} else
-		r = ti->type->map(ti, clone);
+	}
 
 	switch (r) {
 	case DM_MAPIO_SUBMITTED:
Index: linux-2.6/drivers/md/dm.h
===================================================================
--- linux-2.6.orig/drivers/md/dm.h
+++ linux-2.6/drivers/md/dm.h
@@ -188,9 +188,11 @@ void dm_kobject_release(struct kobject *
 /*
  * Targets for linear and striped mappings
  */
+int linear_map(struct dm_target *ti, struct bio *bio);
 int dm_linear_init(void);
 void dm_linear_exit(void);
 
+int stripe_map(struct dm_target *ti, struct bio *bio);
 int dm_stripe_init(void);
 void dm_stripe_exit(void);