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dm stripe: optimize sector division

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Optimize sector division: If the number of stripes is a power of two,
we can do shift and mask instead of division.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka 2010-08-12 04:14:21 +01:00 committed by Alasdair G Kergon
parent 65988525ab
commit c96053b767
1 changed files with 18 additions and 5 deletions
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23
drivers/md/dm-stripe.c
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@ -25,6 +25,8 @@ struct stripe {
struct stripe_c {
uint32_t stripes;
int stripes_shift;
sector_t stripes_mask;
/* The size of this target / num. stripes */
sector_t stripe_width;
@ -162,16 +164,21 @@ static int stripe_ctr(struct dm_target *ti, unsigned int argc, char **argv)
/* Set pointer to dm target; used in trigger_event */
sc->ti = ti;
sc->stripes = stripes;
sc->stripe_width = width;
if (stripes & (stripes - 1))
sc->stripes_shift = -1;
else {
sc->stripes_shift = ffs(stripes) - 1;
sc->stripes_mask = ((sector_t) stripes) - 1;
}
ti->split_io = chunk_size;
ti->num_flush_requests = stripes;
sc->chunk_shift = ffs(chunk_size) - 1;
sc->chunk_mask = ((sector_t) chunk_size) - 1;
for (sc->chunk_shift = 0; chunk_size; sc->chunk_shift++)
chunk_size >>= 1;
sc->chunk_shift--;
/*
* Get the stripe destinations.
@ -213,7 +220,13 @@ static void stripe_map_sector(struct stripe_c *sc, sector_t sector,
sector_t offset = dm_target_offset(sc->ti, sector);
sector_t chunk = offset >> sc->chunk_shift;
*stripe = sector_div(chunk, sc->stripes);
if (sc->stripes_shift < 0)
*stripe = sector_div(chunk, sc->stripes);
else {
*stripe = chunk & sc->stripes_mask;
chunk >>= sc->stripes_shift;
}
*result = (chunk << sc->chunk_shift) | (offset & sc->chunk_mask);
}