diff options
| author | Bart Van Assche <bvanassche@acm.org> | 2019-08-01 15:50:44 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2019-08-04 21:41:29 -0600 |
| commit | 9cc5169cd478bc596902a57580804f1da3dfd74e (patch) | |
| tree | 98fedd293733a36dae88142eafd518688ada4fbd | |
| parent | 708b25b344fd9bedd02ccc0f8eee71f7006d7d07 (diff) | |
block: Improve physical block alignment of split bios
Consider the following example:
* The logical block size is 4 KB.
* The physical block size is 8 KB.
* max_sectors equals (16 KB >> 9) sectors.
* A non-aligned 4 KB and an aligned 64 KB bio are merged into a single
non-aligned 68 KB bio.
The current behavior is to split such a bio into (16 KB + 16 KB + 16 KB
+ 16 KB + 4 KB). The start of none of these five bio's is aligned to a
physical block boundary.
This patch ensures that such a bio is split into four aligned and
one non-aligned bio instead of being split into five non-aligned bios.
This improves performance because most block devices can handle aligned
requests faster than non-aligned requests.
Since the physical block size is larger than or equal to the logical
block size, this patch preserves the guarantee that the returned
value is a multiple of the logical block size.
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | block/blk-merge.c | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/block/blk-merge.c b/block/blk-merge.c index a6bc08255b1b..48e6725b32ee 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -132,16 +132,29 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q, return bio_split(bio, q->limits.max_write_same_sectors, GFP_NOIO, bs); } +/* + * Return the maximum number of sectors from the start of a bio that may be + * submitted as a single request to a block device. If enough sectors remain, + * align the end to the physical block size. Otherwise align the end to the + * logical block size. This approach minimizes the number of non-aligned + * requests that are submitted to a block device if the start of a bio is not + * aligned to a physical block boundary. + */ static inline unsigned get_max_io_size(struct request_queue *q, struct bio *bio) { unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector); - unsigned mask = queue_logical_block_size(q) - 1; + unsigned max_sectors = sectors; + unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT; + unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT; + unsigned start_offset = bio->bi_iter.bi_sector & (pbs - 1); - /* aligned to logical block size */ - sectors &= ~(mask >> 9); + max_sectors += start_offset; + max_sectors &= ~(pbs - 1); + if (max_sectors > start_offset) + return max_sectors - start_offset; - return sectors; + return sectors & (lbs - 1); } static unsigned get_max_segment_size(const struct request_queue *q, |