dm stripe: optimize chunk_size calculations
dm-stripe is usually used with a chunk size that is a power of two.
Use faster shifts and bit masks in such cases.
stripe_width is already optimized in a similar way.
Signed-off-by: Mikulas Patocka <mpatocka@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 6a20e9e..9e8f4cc 100644
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -31,6 +31,7 @@
sector_t stripe_width;
uint32_t chunk_size;
+ int chunk_size_shift;
/* Needed for handling events */
struct dm_target *ti;
@@ -163,6 +164,10 @@
ti->num_discard_requests = stripes;
sc->chunk_size = chunk_size;
+ if (chunk_size & (chunk_size - 1))
+ sc->chunk_size_shift = -1;
+ else
+ sc->chunk_size_shift = __ffs(chunk_size);
/*
* Get the stripe destinations.
@@ -202,7 +207,14 @@
uint32_t *stripe, sector_t *result)
{
sector_t chunk = dm_target_offset(sc->ti, sector);
- sector_t chunk_offset = sector_div(chunk, sc->chunk_size);
+ sector_t chunk_offset;
+
+ if (sc->chunk_size_shift < 0)
+ chunk_offset = sector_div(chunk, sc->chunk_size);
+ else {
+ chunk_offset = chunk & (sc->chunk_size - 1);
+ chunk >>= sc->chunk_size_shift;
+ }
if (sc->stripes_shift < 0)
*stripe = sector_div(chunk, sc->stripes);
@@ -211,7 +223,12 @@
chunk >>= sc->stripes_shift;
}
- *result = (chunk * sc->chunk_size) + chunk_offset;
+ if (sc->chunk_size_shift < 0)
+ chunk *= sc->chunk_size;
+ else
+ chunk <<= sc->chunk_size_shift;
+
+ *result = chunk + chunk_offset;
}
static void stripe_map_range_sector(struct stripe_c *sc, sector_t sector,
@@ -225,7 +242,10 @@
/* round down */
sector = *result;
- *result -= sector_div(sector, sc->chunk_size);
+ if (sc->chunk_size_shift < 0)
+ *result -= sector_div(sector, sc->chunk_size);
+ else
+ *result = sector & ~(sector_t)(sc->chunk_size - 1);
if (target_stripe < stripe)
*result += sc->chunk_size; /* next chunk */