linux-kernel - [RFC PATCH 2/2] Revert "mq-deadline: Fix request accounting"

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Date:   Fri, 27 Aug 2021 12:41:43 +0000
From:   Niklas Cassel <Niklas.Cassel@....com>
To:     Jens Axboe <axboe@...nel.dk>
CC:     Bart Van Assche <bvanassche@....org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Paolo Valente <paolo.valente@...aro.org>,
        Niklas Cassel <Niklas.Cassel@....com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 2/2] Revert "mq-deadline: Fix request accounting"

From: Niklas Cassel <niklas.cassel@....com>

This reverts commit b6d2b054e8baaee53fd2d4854c63cbf0f2c6262a.

There is no longer any need to perform any workaround private data magic
in order to track if a request was inserted to the scheduler or not.

blk-mq will no longer call .finish_request() for requests that were
never inserted to the scheduler.

This patch also didn't handle requeues properly, so it would have
required additional private data magic if it wasn't reverted.

Signed-off-by: Niklas Cassel <niklas.cassel@....com>
---
 block/mq-deadline.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 36920670dccc..a5d171b54f8e 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -682,7 +682,6 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
 
 	prio = ioprio_class_to_prio[ioprio_class];
 	dd_count(dd, inserted, prio);
-	rq->elv.priv[0] = (void *)(uintptr_t)1;
 
 	if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
 		blk_mq_free_requests(&free);
@@ -731,10 +730,12 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
 	spin_unlock(&dd->lock);
 }
 
-/* Callback from inside blk_mq_rq_ctx_init(). */
+/*
+ * Nothing to do here. This is defined only to ensure that .finish_request
+ * method is called upon request completion.
+ */
 static void dd_prepare_request(struct request *rq)
 {
-	rq->elv.priv[0] = NULL;
 }
 
 /*
@@ -761,14 +762,7 @@ static void dd_finish_request(struct request *rq)
 	const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
 	struct dd_per_prio *per_prio = &dd->per_prio[prio];
 
-	/*
-	 * The block layer core may call dd_finish_request() without having
-	 * called dd_insert_requests(). Hence only update statistics for
-	 * requests for which dd_insert_requests() has been called. See also
-	 * blk_mq_request_bypass_insert().
-	 */
-	if (rq->elv.priv[0])
-		dd_count(dd, completed, prio);
+	dd_count(dd, completed, prio);
 
 	if (blk_queue_is_zoned(q)) {
 		unsigned long flags;
-- 
2.31.1