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 6a20e9ea0bfb0883f053c48e5e0c5d5558f01a74..9e8f4cc63d6cf660e3b698bcaa6e6b76d3c49aa8 100644 (file)
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -31,6 +31,7 @@ struct stripe_c {
        sector_t stripe_width;
 
        uint32_t chunk_size;
+       int chunk_size_shift;
 
        /* Needed for handling events */
        struct dm_target *ti;
@@ -163,6 +164,10 @@ static int stripe_ctr(struct dm_target *ti, unsigned int argc, char **argv)
        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 @@ static void stripe_map_sector(struct stripe_c *sc, sector_t sector,
                              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 @@ static void stripe_map_sector(struct stripe_c *sc, sector_t sector,
                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 @@ static void stripe_map_range_sector(struct stripe_c *sc, sector_t sector,
 
        /* 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 */