linux-kernel - [PATCH AUTOSEL 5.8 095/132] block: Consider only dispatched requests for inflight statistic

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Date:   Mon, 26 Oct 2020 19:51:27 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Gabriel Krisman Bertazi <krisman@...labora.com>,
        Omar Sandoval <osandov@...com>, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>, linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 5.8 095/132] block: Consider only dispatched requests for inflight statistic

From: Gabriel Krisman Bertazi <krisman@...labora.com>

[ Upstream commit a926c7afffcc0f2e35e6acbccb16921bacf34617 ]

According to Documentation/block/stat.rst, inflight should not include
I/O requests that are in the queue but not yet dispatched to the device,
but blk-mq identifies as inflight any request that has a tag allocated,
which, for queues without elevator, happens at request allocation time
and before it is queued in the ctx (default case in blk_mq_submit_bio).

In addition, current behavior is different for queues with elevator from
queues without it, since for the former the driver tag is allocated at
dispatch time.  A more precise approach would be to only consider
requests with state MQ_RQ_IN_FLIGHT.

This effectively reverts commit 6131837b1de6 ("blk-mq: count allocated
but not started requests in iostats inflight") to consolidate blk-mq
behavior with itself (elevator case) and with original documentation,
but it differs from the behavior used by the legacy path.

This version differs from v1 by using blk_mq_rq_state to access the
state attribute.  Avoid using blk_mq_request_started, which was
suggested, since we don't want to include MQ_RQ_COMPLETE.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
Cc: Omar Sandoval <osandov@...com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-mq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8e623e0282757..88b0dc0034cff 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -103,7 +103,7 @@ static bool blk_mq_check_inflight(struct blk_mq_hw_ctx *hctx,
 {
 	struct mq_inflight *mi = priv;

-	if (rq->part == mi->part)
+	if (rq->part == mi->part && blk_mq_rq_state(rq) == MQ_RQ_IN_FLIGHT)
 		mi->inflight[rq_data_dir(rq)]++;

 	return true;
-- 
2.25.1