block: Do not pull requests from the scheduler when we cannot dispatch them

[linux-2.6-microblaze.git] / block / blk-mq-sched.c

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 045b687..a9182d2 100644 (file)
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -168,9 +168,19 @@ static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
                 * in blk_mq_dispatch_rq_list().
                 */
                list_add_tail(&rq->queuelist, &rq_list);
+               count++;
                if (rq->mq_hctx != hctx)
                        multi_hctxs = true;
-       } while (++count < max_dispatch);
+
+               /*
+                * If we cannot get tag for the request, stop dequeueing
+                * requests from the IO scheduler. We are unlikely to be able
+                * to submit them anyway and it creates false impression for
+                * scheduling heuristics that the device can take more IO.
+                */
+               if (!blk_mq_get_driver_tag(rq))
+                       break;
+       } while (count < max_dispatch);
 
        if (!count) {
                if (run_queue)