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authorMikulas Patocka <mpatocka@redhat.com>2010-08-12 04:14:21 +0100
committerAlasdair G Kergon <agk@redhat.com>2010-08-12 04:14:21 +0100
commitc96053b767d494d7c30e2be68097ac9defa9403f (patch)
treeb66f185ffd58538f6107f3acf3af38b8aecd7f8a /drivers/md/dm-stripe.c
parent65988525abde0b0a5833c4e20f32967184a5dcf0 (diff)
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>
Diffstat (limited to 'drivers/md/dm-stripe.c')
-rw-r--r--drivers/md/dm-stripe.c23
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);
}