dm stripe: optimize sector division

Optimize sector division: If the number of stripes is a power of two,
we can do shift and mask instead of division.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 18 insertions, 5 deletions

diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index e2ad1ae5268d..1559fdfd2073 100644
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -25,6 +25,8 @@ struct stripe {
 
 struct stripe_c {
         uint32_t stripes;
+        int stripes_shift;
+        sector_t stripes_mask;
 
         /* The size of this target / num. stripes */
         sector_t stripe_width;
@@ -162,16 +164,21 @@ static int stripe_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
         /* Set pointer to dm target; used in trigger_event */
         sc->ti = ti;
-
         sc->stripes = stripes;
         sc->stripe_width = width;
+
+        if (stripes & (stripes - 1))
+                sc->stripes_shift = -1;
+        else {
+                sc->stripes_shift = ffs(stripes) - 1;
+                sc->stripes_mask = ((sector_t) stripes) - 1;
+        }
+
         ti->split_io = chunk_size;
         ti->num_flush_requests = stripes;
 
+        sc->chunk_shift = ffs(chunk_size) - 1;
         sc->chunk_mask = ((sector_t) chunk_size) - 1;
-        for (sc->chunk_shift = 0; chunk_size; sc->chunk_shift++)
-                chunk_size >>= 1;
-        sc->chunk_shift--;
 
         /*
          * Get the stripe destinations.
@@ -213,7 +220,13 @@ static void stripe_map_sector(struct stripe_c *sc, sector_t sector,
         sector_t offset = dm_target_offset(sc->ti, sector);
         sector_t chunk = offset >> sc->chunk_shift;
 
-        *stripe = sector_div(chunk, sc->stripes);
+        if (sc->stripes_shift < 0)
+                *stripe = sector_div(chunk, sc->stripes);
+        else {
+                *stripe = chunk & sc->stripes_mask;
+                chunk >>= sc->stripes_shift;
+        }
+
         *result = (chunk << sc->chunk_shift) | (offset & sc->chunk_mask);
 }