[PATCH v2] block: rename need_dispatch to piecemeal_dispatch in blk-mq sched

[Guixin Liu <kanie@linux.alibaba.com>]

The local boolean in __blk_mq_sched_dispatch_requests() decides whether
to fall back to the per-ctx round-robin path (blk_mq_do_dispatch_ctx())
instead of the batch flush path (blk_mq_flush_busy_ctxs()).  The whole
function is about dispatching anyway, so the name "need_dispatch" is
not particularly informative and can mislead readers into thinking that
a false value means "skip dispatching".

Rename it to "piecemeal_dispatch" to match the comment right above the
check ("dequeue request one by one from sw queue if queue is busy")
and to convey the actual intent: take the piecemeal, fair, one-at-a-time
path either when we just drained hctx->dispatch (so the device has
recently pushed back) or when the dispatch_busy EWMA still indicates
congestion.  The fast batch path is only taken when neither signal
suggests recent backpressure.

No functional change.

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
---
v2 -> v1:
- Change cautious_dispatch to piecemeal_dispatch, the advice from Jens.

 block/blk-mq-sched.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 0a00f5a76f5a..14dacf99e148 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -267,7 +267,7 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 
 static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 {
-	bool need_dispatch = false;
+	bool piecemeal_dispatch = false;
 	LIST_HEAD(rq_list);
 
 	/*
@@ -298,16 +298,16 @@ static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 		blk_mq_sched_mark_restart_hctx(hctx);
 		if (!blk_mq_dispatch_rq_list(hctx, &rq_list, true))
 			return 0;
-		need_dispatch = true;
+		piecemeal_dispatch = true;
 	} else {
-		need_dispatch = hctx->dispatch_busy;
+		piecemeal_dispatch = hctx->dispatch_busy;
 	}
 
 	if (hctx->queue->elevator)
 		return blk_mq_do_dispatch_sched(hctx);
 
 	/* dequeue request one by one from sw queue if queue is busy */
-	if (need_dispatch)
+	if (piecemeal_dispatch)
 		return blk_mq_do_dispatch_ctx(hctx);
 	blk_mq_flush_busy_ctxs(hctx, &rq_list);
 	blk_mq_dispatch_rq_list(hctx, &rq_list, true);
-- 
2.43.7