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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>
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Mikulas Patocka authored and Alasdair G Kergon committed Aug 12, 2010
1 parent 6598852 commit c96053b
Showing 1 changed file with 18 additions and 5 deletions.
23 changes: 18 additions & 5 deletions drivers/md/dm-stripe.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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.
Expand Down Expand Up @@ -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);
}

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