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dm thin: optimize power of two block size

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dm-thin will be most likely used with a block size that is a power of
two. So it should be optimized for this case.

This patch changes division and modulo operations to shifts and bit
masks if block size is a power of two.

A test that bi_sector is divisible by a block size is removed from
io_overlaps_block. Device mapper never sends bios that span a block
boundary. Consequently, if we tested that bi_size is equivalent to block
size, bi_sector must already be on a block boundary.

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 15:08:03 +01:00 committed by Alasdair G Kergon
parent 4929630901
commit f9a8e0cd26
1 changed files with 16 additions and 7 deletions
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17
drivers/md/dm-thin.c
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@ -512,6 +512,7 @@ struct pool {
dm_block_t low_water_blocks;
uint32_t sectors_per_block;
int sectors_per_block_shift;
struct pool_features pf;
unsigned low_water_triggered:1; /* A dm event has been sent */
@ -679,7 +680,10 @@ static dm_block_t get_bio_block(struct thin_c *tc, struct bio *bio)
{
sector_t block_nr = bio->bi_sector;
if (tc->pool->sectors_per_block_shift < 0)
(void) sector_div(block_nr, tc->pool->sectors_per_block);
else
block_nr >>= tc->pool->sectors_per_block_shift;
return block_nr;
}
@ -690,8 +694,12 @@ static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
sector_t bi_sector = bio->bi_sector;
bio->bi_bdev = tc->pool_dev->bdev;
if (tc->pool->sectors_per_block_shift < 0)
bio->bi_sector = (block * pool->sectors_per_block) +
sector_div(bi_sector, pool->sectors_per_block);
else
bio->bi_sector = (block << pool->sectors_per_block_shift) |
(bi_sector & (pool->sectors_per_block - 1));
}
static void remap_to_origin(struct thin_c *tc, struct bio *bio)
@ -936,10 +944,7 @@ static void process_prepared(struct pool *pool, struct list_head *head,
*/
static int io_overlaps_block(struct pool *pool, struct bio *bio)
{
sector_t bi_sector = bio->bi_sector;
return !sector_div(bi_sector, pool->sectors_per_block) &&
(bio->bi_size == (pool->sectors_per_block << SECTOR_SHIFT));
return bio->bi_size == (pool->sectors_per_block << SECTOR_SHIFT);
}
static int io_overwrites_block(struct pool *pool, struct bio *bio)
@ -1721,6 +1726,10 @@ static struct pool *pool_create(struct mapped_device *pool_md,
pool->pmd = pmd;
pool->sectors_per_block = block_size;
if (block_size & (block_size - 1))
pool->sectors_per_block_shift = -1;
else
pool->sectors_per_block_shift = __ffs(block_size);
pool->low_water_blocks = 0;
pool_features_init(&pool->pf);
pool->prison = prison_create(PRISON_CELLS);