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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>
This commit is contained in:
Mikulas Patocka 2012-07-27 15:08:02 +01:00 committed by Alasdair G Kergon
parent 8f069b41bc
commit 33d07c0dfa
1 changed files with 23 additions and 3 deletions
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26
drivers/md/dm-stripe.c
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@ -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 */