block: change the tag sync vs async restriction logic
Make them fully share the tag space, but disallow async requests using
the last any two slots.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-tag.c b/block/blk-tag.c
index c260f7c..2e5cfeb 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -336,7 +336,7 @@
int blk_queue_start_tag(struct request_queue *q, struct request *rq)
{
struct blk_queue_tag *bqt = q->queue_tags;
- unsigned max_depth, offset;
+ unsigned max_depth;
int tag;
if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
@@ -355,13 +355,16 @@
* 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;
+ if (!rq_is_sync(rq) && max_depth > 1) {
+ max_depth -= 2;
+ if (!max_depth)
+ max_depth = 1;
+ if (q->in_flight[0] > max_depth)
+ return 1;
+ }
do {
- tag = find_next_zero_bit(bqt->tag_map, max_depth, offset);
+ tag = find_first_zero_bit(bqt->tag_map, max_depth);
if (tag >= max_depth)
return 1;
