aboutsummaryrefslogtreecommitdiff
path: root/block
diff options
context:
space:
mode:
authorJan Kara <jack@suse.cz>2013-06-28 21:32:27 +0200
committerJens Axboe <axboe@kernel.dk>2013-06-28 21:32:27 +0200
commita6b3f7614ca690e49e934c291f707b0c19312194 (patch)
tree1b22a33b78bafcfca8eb7509b7104eaff3b0ab99 /block
parenta5faeaf9109578e65e1a32e2a3e76c8b47e7dcb6 (diff)
downloadlinux-linaro-stable-a6b3f7614ca690e49e934c291f707b0c19312194.tar.gz
block: Reserve only one queue tag for sync IO if only 3 tags are available
In case a device has three tags available we still reserve two of them for sync IO. That leaves only a single tag for async IO such as writeback from flusher thread which results in poor performance. Allow async IO to consume two tags in case queue has three tag availabe to get a decent async write performance. This patch improves streaming write performance on a machine with such disk from ~21 MB/s to ~52 MB/s. Also postmark throughput in presence of streaming writer improves from 8 to 12 transactions per second so sync IO doesn't seem to be harmed in presence of heavy async writer. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r--block/blk-tag.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/block/blk-tag.c b/block/blk-tag.c
index cc345e1d8d4e..3f33d8672268 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -348,9 +348,16 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
*/
max_depth = bqt->max_depth;
if (!rq_is_sync(rq) && max_depth > 1) {
- max_depth -= 2;
- if (!max_depth)
+ switch (max_depth) {
+ case 2:
max_depth = 1;
+ break;
+ case 3:
+ max_depth = 2;
+ break;
+ default:
+ max_depth -= 2;
+ }
if (q->in_flight[BLK_RW_ASYNC] > max_depth)
return 1;
}