Optimize sector division
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>
---
drivers/md/dm-stripe.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
Index: linux-2.6.35-rc6-fast/drivers/md/dm-stripe.c
===================================================================
--- linux-2.6.35-rc6-fast.orig/drivers/md/dm-stripe.c 2010-07-28 00:01:04.000000000 +0200
+++ linux-2.6.35-rc6-fast/drivers/md/dm-stripe.c 2010-07-28 00:06:19.000000000 +0200
@@ -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;
@@ -212,7 +217,11 @@ 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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