dm thin: optimize power of two block size
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>
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 8286492..93e3e54 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -512,6 +512,7 @@
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 @@
{
sector_t block_nr = bio->bi_sector;
- (void) sector_div(block_nr, tc->pool->sectors_per_block);
+ 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 @@
sector_t bi_sector = bio->bi_sector;
bio->bi_bdev = tc->pool_dev->bdev;
- bio->bi_sector = (block * pool->sectors_per_block) +
- sector_div(bi_sector, pool->sectors_per_block);
+ 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 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 @@
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);