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>
diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index e2ad1ae..1559fdf 100644
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -25,6 +25,8 @@
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 @@
/* 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 @@
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);
}