diff options
| -rw-r--r-- | block/blk-tag.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/block/blk-tag.c b/block/blk-tag.c index 8a99688eb1b..c0d419e84ce 100644 --- a/block/blk-tag.c +++ b/block/blk-tag.c @@ -337,6 +337,7 @@ EXPORT_SYMBOL(blk_queue_end_tag); int blk_queue_start_tag(struct request_queue *q, struct request *rq) { struct blk_queue_tag *bqt = q->queue_tags; + unsigned max_depth, offset; int tag; if (unlikely((rq->cmd_flags & REQ_QUEUED))) { @@ -350,10 +351,19 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq) /* * Protect against shared tag maps, as we may not have exclusive * access to the tag map. + * + * We reserve a few tags just for sync IO, since we don't want + * to starve sync IO on behalf of flooding async IO. */ + max_depth = bqt->max_depth; + if (rq_is_sync(rq)) + offset = 0; + else + offset = max_depth >> 2; + do { - tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth); - if (tag >= bqt->max_depth) + tag = find_next_zero_bit(bqt->tag_map, max_depth, offset); + if (tag >= max_depth) return 1; } while (test_and_set_bit_lock(tag, bqt->tag_map)); |