blk-mq: introduce .get_budget and .put_budget in blk_mq_ops
For SCSI devices, there is often a per-request-queue depth, which needs
to be respected before queuing one request.
Currently blk-mq always dequeues the request first, then calls
.queue_rq() to dispatch the request to lld. One obvious issue with this
approach is that I/O merging may not be successful, because when the
per-request-queue depth can't be respected, .queue_rq() has to return
BLK_STS_RESOURCE, and then this request has to stay in hctx->dispatch
list. This means it never gets a chance to be merged with other IO.
This patch introduces .get_budget and .put_budget callback in blk_mq_ops,
then we can try to get reserved budget first before dequeuing request.
If the budget for queueing I/O can't be satisfied, we don't need to
dequeue request at all. Hence the request can be left in the IO
scheduler queue, for more merging opportunities.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index be29ba8..8e525e6 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -89,31 +89,57 @@
return false;
}
-static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
+/* return true if hctx need to run again */
+static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
struct elevator_queue *e = q->elevator;
LIST_HEAD(rq_list);
do {
- struct request *rq = e->type->ops.mq.dispatch_request(hctx);
+ struct request *rq;
+ blk_status_t ret;
- if (!rq)
+ if (e->type->ops.mq.has_work &&
+ !e->type->ops.mq.has_work(hctx))
break;
+
+ ret = blk_mq_get_dispatch_budget(hctx);
+ if (ret == BLK_STS_RESOURCE)
+ return true;
+
+ rq = e->type->ops.mq.dispatch_request(hctx);
+ if (!rq) {
+ blk_mq_put_dispatch_budget(hctx);
+ break;
+ } else if (ret != BLK_STS_OK) {
+ blk_mq_end_request(rq, ret);
+ continue;
+ }
+
+ /*
+ * Now this rq owns the budget which has to be released
+ * if this rq won't be queued to driver via .queue_rq()
+ * in blk_mq_dispatch_rq_list().
+ */
list_add(&rq->queuelist, &rq_list);
- } while (blk_mq_dispatch_rq_list(q, &rq_list));
+ } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
+
+ return false;
}
-void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
+/* return true if hw queue need to be run again */
+bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
struct elevator_queue *e = q->elevator;
const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
LIST_HEAD(rq_list);
+ bool run_queue = false;
/* RCU or SRCU read lock is needed before checking quiesced flag */
if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
- return;
+ return false;
hctx->run++;
@@ -143,14 +169,23 @@
*/
if (!list_empty(&rq_list)) {
blk_mq_sched_mark_restart_hctx(hctx);
- if (blk_mq_dispatch_rq_list(q, &rq_list) && has_sched_dispatch)
- blk_mq_do_dispatch_sched(hctx);
+ if (blk_mq_dispatch_rq_list(q, &rq_list, false) &&
+ has_sched_dispatch)
+ run_queue = blk_mq_do_dispatch_sched(hctx);
} else if (has_sched_dispatch) {
- blk_mq_do_dispatch_sched(hctx);
+ run_queue = blk_mq_do_dispatch_sched(hctx);
} else {
blk_mq_flush_busy_ctxs(hctx, &rq_list);
- blk_mq_dispatch_rq_list(q, &rq_list);
+ blk_mq_dispatch_rq_list(q, &rq_list, false);
}
+
+ if (run_queue && !blk_mq_sched_needs_restart(hctx) &&
+ !test_bit(BLK_MQ_S_TAG_WAITING, &hctx->state)) {
+ blk_mq_sched_mark_restart_hctx(hctx);
+ return true;
+ }
+
+ return false;
}
bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,