linux-kernel - [PATCH] block: account statistics for passthrough requests

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Date:   Thu, 10 Oct 2019 17:36:26 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Cc:     Stephen Bates <sbates@...thlin.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH] block: account statistics for passthrough requests

Presently, passthrough requests are not accounted for because
blk_do_io_stat() expressly rejects them. Based on some digging
in the history, this doesn't seem like a concious decision but
one that evolved from the change from blk_fs_request() to
blk_rq_is_passthrough().

To support this, call blk_account_io_start() in blk_execute_rq_nowait()
and remove the passthrough check in blk_do_io_stat().

Link: https://lore.kernel.org/linux-block/20191010100526.GA27209@lst.de/
Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Christoph Hellwig <hch@....de>
---

This change is needed for the NVMe-of passthru work that is in progress.
Christoph suggested sending it as its own patch. (See the link
in the commit message for more information.)

 block/blk-exec.c | 2 ++
 block/blk.h      | 7 ++-----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/block/blk-exec.c b/block/blk-exec.c
index 1db44ca0f4a6..e20a852ae432 100644
--- a/block/blk-exec.c
+++ b/block/blk-exec.c
@@ -55,6 +55,8 @@ void blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk,
 	rq->rq_disk = bd_disk;
 	rq->end_io = done;

+	blk_account_io_start(rq, true);
+
 	/*
 	 * don't check dying flag for MQ because the request won't
 	 * be reused after dying flag is set
diff --git a/block/blk.h b/block/blk.h
index 47fba9362e60..2bea40180b6f 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -242,14 +242,11 @@ int blk_dev_init(void);
  * Contribute to IO statistics IFF:
  *
  *	a) it's attached to a gendisk, and
- *	b) the queue had IO stats enabled when this request was started, and
- *	c) it's a file system request
+ *	b) the queue had IO stats enabled when this request was started
  */
 static inline bool blk_do_io_stat(struct request *rq)
 {
-	return rq->rq_disk &&
-	       (rq->rq_flags & RQF_IO_STAT) &&
-		!blk_rq_is_passthrough(rq);
+	return rq->rq_disk && (rq->rq_flags & RQF_IO_STAT);
 }

 static inline void req_set_nomerge(struct request_queue *q, struct request *req)
--
2.20.1