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Commit 33d07c0d authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 8f069b41

drivers/md/dm-stripe.c

+23 −3
Original line number Diff line number Diff line
@@ -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;

	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 */