Hi
This patch optimizes dm-stripe if chunk_size is a power of two. It should
be applied after "dm-stripe-support-for-non-power-of-2-chunksize.patch".
Mikulas
---
dm-stripe: Optimize chunk_size divisions and modulos
dm-stripe is usually used with a chunk size that is a power of two.
Previous code used slow divide and modulo operations with a power-of-two
chunk size. This patch changes it to use faster shifts and bit masks.
stripe_width is already optimized in a similar way.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm-stripe.c | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
Index: linux-3.4.2-fast/drivers/md/dm-stripe.c
===================================================================
--- linux-3.4.2-fast.orig/drivers/md/dm-stripe.c 2012-06-18 11:39:36.000000000 +0200
+++ linux-3.4.2-fast/drivers/md/dm-stripe.c 2012-06-18 12:52:40.000000000 +0200
@@ -32,6 +32,7 @@ struct stripe_c {
sector_t stripe_width;
uint32_t chunk_size;
+ int chunk_size_shift;
/* Needed for handling events */
struct dm_target *ti;
@@ -170,6 +171,10 @@ static int stripe_ctr(struct dm_target *
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.
@@ -209,7 +214,14 @@ static void stripe_map_sector(struct str
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);
@@ -218,7 +230,12 @@ static void stripe_map_sector(struct str
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,
@@ -232,7 +249,10 @@ static void stripe_map_range_sector(stru
/* 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 */
--
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