Patch "blk-mq-sched: dispatch from scheduler IFF progress is made in ->dispatch" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

    blk-mq-sched: dispatch from scheduler IFF progress is made in ->dispatch

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
blk-mq-sched-dispatch-from-scheduler-iff-progress-is-made-in-dispatch.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ming Lei <[email protected]>
Date: Sat, 14 Oct 2017 17:22:25 +0800
Subject: blk-mq-sched: dispatch from scheduler IFF progress is made in ->dispatch

From: Ming Lei <[email protected]>

[ Upstream commit 5e3d02bbafad38975099b5848f5ebadedcf7bb7e ]

When the hw queue is busy, we shouldn't take requests from the scheduler queue any more, otherwise it is difficult to do IO merge.

This patch fixes the awful IO performance on some SCSI devices(lpfc, qla2xxx, ...) when mq-deadline/kyber is used by not taking requests if hw queue is busy.

---
 block/blk-mq-sched.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

@@ -94,7 +94,7 @@ void blk_mq_sched_dispatch_requests(stru
 	struct request_queue *q = hctx->queue;
 	struct elevator_queue *e = q->elevator;
 	const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
-	bool did_work = false;
+	bool do_sched_dispatch = true;
 	LIST_HEAD(rq_list);
 
 	/* RCU or SRCU read lock is needed before checking quiesced flag */

@@ -125,18 +125,18 @@ void blk_mq_sched_dispatch_requests(stru
 	 */
 	if (!list_empty(&rq_list)) {
 		blk_mq_sched_mark_restart_hctx(hctx);
-		did_work = blk_mq_dispatch_rq_list(q, &rq_list);
+		do_sched_dispatch = blk_mq_dispatch_rq_list(q, &rq_list);
 	} else if (!has_sched_dispatch) {
 		blk_mq_flush_busy_ctxs(hctx, &rq_list);
 		blk_mq_dispatch_rq_list(q, &rq_list);
 	}
 
 	/*
-	 * We want to dispatch from the scheduler if we had no work left
-	 * on the dispatch list, OR if we did have work but weren't able
-	 * to make progress.
+	 * We want to dispatch from the scheduler if there was nothing
+	 * on the dispatch list or we were able to dispatch from the
+	 * dispatch list.
 	 */
-	if (!did_work && has_sched_dispatch) {
+	if (do_sched_dispatch && has_sched_dispatch) {
 		do {
 			struct request *rq;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/scsi-core-fix-a-scsi_show_rq-null-pointer-dereference.patch queue-4.14/blk-mq-sched-dispatch-from-scheduler-iff-progress-is-made-in-dispatch.patch