Commit c96053b7 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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dm stripe: optimize sector division 



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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 65988525

drivers/md/dm-stripe.c

+18 −5
Original line number Diff line number Diff line
@@ -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;



	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);

}