From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Optimize sector division --- if the number of stripes is a power of two,
we don't have to do expensive division and can do shift and mask instead.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
---
drivers/md/dm-stripe.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
v2: minor code cleanup in stripe_map_sector
Index: linux-2.6-block/drivers/md/dm-stripe.c
===================================================================
--- linux-2.6-block.orig/drivers/md/dm-stripe.c
+++ linux-2.6-block/drivers/md/dm-stripe.c
@@ -25,6 +25,7 @@ struct stripe {
struct stripe_c {
uint32_t stripes;
+ int stripes_shift;
/* The size of this target / num. stripes */
sector_t stripe_width;
@@ -164,6 +165,10 @@ static int stripe_ctr(struct dm_target *
sc->ti = ti;
sc->stripes = stripes;
+ if (!(stripes & (stripes - 1)))
+ sc->stripes_shift = ffs(stripes) - 1;
+ else
+ sc->stripes_shift = -1;
sc->stripe_width = width;
ti->split_io = chunk_size;
ti->num_flush_requests = stripes;
@@ -213,7 +218,12 @@ static void stripe_map_sector(struct str
{
sector_t offset = sector - sc->ti->begin;
sector_t chunk = offset >> sc->chunk_shift;
- *stripe = sector_div(chunk, sc->stripes);
+
+ if (likely(sc->stripes_shift >= 0)) {
+ *stripe = chunk & ((1 << sc->stripes_shift) - 1);
+ chunk >>= sc->stripes_shift;
+ } else
+ *stripe = sector_div(chunk, sc->stripes);
*result = (chunk << sc->chunk_shift) | (offset & sc->chunk_mask);
}
--
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