[PATCHv2 0/2] block, nvme: enable passthrough iostats

[PATCHv2 0/2] block, nvme: enable passthrough iostats

[Keith Busch]

From: Keith Busch <kbusch@kernel.org>

v1->v2:

  Split the block and nvme parts into separate patches.

  Fixed up the nvme driver to ensure passthrough commands go through the
  multipath start/end functions.

  Have the helper function take a request_queue parameter since the
  queue accumulating the stats for multipath isn't the same as the
  request's queue. 

Keith Busch (2):
  block: export passthrough stats enabled
  nvme: add support multipath passthrough iostats

 block/blk-mq.c                | 32 +-------------------------------
 drivers/nvme/host/ioctl.c     |  4 ++++
 drivers/nvme/host/multipath.c |  5 ++++-
 include/linux/blk-mq.h        | 30 ++++++++++++++++++++++++++++++
 4 files changed, 39 insertions(+), 32 deletions(-)

-- 
2.53.0-Meta

[PATCHv2 1/2] block: export passthrough stats enabled

[Keith Busch]

From: Keith Busch <kbusch@kernel.org>

A user can enable io accounting for passthrough requests, so export the
helper that checks if the request should be tracked. This will enable
stacking drivers to to report iostats for passthrough workloads.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 block/blk-mq.c         | 32 +-------------------------------
 include/linux/blk-mq.h | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 31 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 28c2d931e75ea..48115e1d9d6a8 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1088,43 +1088,13 @@ static inline void blk_account_io_done(struct request *req, u64 now)
 	}
 }
 
-static inline bool blk_rq_passthrough_stats(struct request *req)
-{
-	struct bio *bio = req->bio;
-
-	if (!blk_queue_passthrough_stat(req->q))
-		return false;
-
-	/* Requests without a bio do not transfer data. */
-	if (!bio)
-		return false;
-
-	/*
-	 * Stats are accumulated in the bdev, so must have one attached to a
-	 * bio to track stats. Most drivers do not set the bdev for passthrough
-	 * requests, but nvme is one that will set it.
-	 */
-	if (!bio->bi_bdev)
-		return false;
-
-	/*
-	 * We don't know what a passthrough command does, but we know the
-	 * payload size and data direction. Ensuring the size is aligned to the
-	 * block size filters out most commands with payloads that don't
-	 * represent sector access.
-	 */
-	if (blk_rq_bytes(req) & (bdev_logical_block_size(bio->bi_bdev) - 1))
-		return false;
-	return true;
-}
-
 static inline void blk_account_io_start(struct request *req)
 {
 	trace_block_io_start(req);
 
 	if (!blk_queue_io_stat(req->q))
 		return;
-	if (blk_rq_is_passthrough(req) && !blk_rq_passthrough_stats(req))
+	if (blk_rq_is_passthrough(req) && !blk_rq_passthrough_stats(req, req->q))
 		return;
 
 	req->rq_flags |= RQF_IO_STAT;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 18a2388ba581d..25931a8076d2a 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -1243,4 +1243,34 @@ static inline int blk_rq_map_sg(struct request *rq, struct scatterlist *sglist)
 }
 void blk_dump_rq_flags(struct request *, char *);
 
+static inline bool blk_rq_passthrough_stats(struct request *req,
+					    struct request_queue *q)
+{
+	struct bio *bio = req->bio;
+
+	if (!blk_queue_passthrough_stat(q))
+		return false;
+
+	/* Requests without a bio do not transfer data. */
+	if (!bio)
+		return false;
+
+	/*
+	 * Stats are accumulated in the bdev, so must have one attached to a
+	 * bio to track stats. Most drivers do not set the bdev for passthrough
+	 * requests, but nvme is one that will set it.
+	 */
+	if (!bio->bi_bdev)
+		return false;
+
+	/*
+	 * We don't know what a passthrough command does, but we know the
+	 * payload size and data direction. Ensuring the size is aligned to the
+	 * block size filters out most commands with payloads that don't
+	 * represent sector access.
+	 */
+	if (blk_rq_bytes(req) & (bdev_logical_block_size(bio->bi_bdev) - 1))
+		return false;
+	return true;
+}
 #endif /* BLK_MQ_H */
-- 
2.53.0-Meta

Re: [PATCHv2 1/2] block: export passthrough stats enabled

[Nilay Shroff]

On 5/26/26 9:09 PM, Keith Busch wrote:
> From: Keith Busch<kbusch@kernel.org>
> 
> A user can enable io accounting for passthrough requests, so export the
> helper that checks if the request should be tracked. This will enable
> stacking drivers to to report iostats for passthrough workloads.
> 
> Signed-off-by: Keith Busch<kbusch@kernel.org>
> ---
>   block/blk-mq.c         | 32 +-------------------------------
>   include/linux/blk-mq.h | 30 ++++++++++++++++++++++++++++++
>   2 files changed, 31 insertions(+), 31 deletions(-)

Looks good to me.
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>

Re: [PATCHv2 1/2] block: export passthrough stats enabled

[Nitesh Shetty]

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On 26/05/26 08:39AM, Keith Busch wrote:
>From: Keith Busch <kbusch@kernel.org>
>
>A user can enable io accounting for passthrough requests, so export the
>helper that checks if the request should be tracked. This will enable
>stacking drivers to to report iostats for passthrough workloads.
>
>Signed-off-by: Keith Busch <kbusch@kernel.org>

Reviewed-by: Nitesh Shetty <nj.shetty@samsung.com>

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Re: [PATCHv2 1/2] block: export passthrough stats enabled

[Christoph Hellwig]

> +static inline bool blk_rq_passthrough_stats(struct request *req,
> +					    struct request_queue *q)

The kerneldoc requested last time would be really nice to have.
Also, now that this is a public API killing the q argument and
just using req->q would make the API easier to understand.

Re: [PATCHv2 1/2] block: export passthrough stats enabled

[Keith Busch]

On Wed, May 27, 2026 at 03:14:58PM +0200, Christoph Hellwig wrote:
> > +static inline bool blk_rq_passthrough_stats(struct request *req,
> > +					    struct request_queue *q)
> 
> The kerneldoc requested last time would be really nice to have.
> Also, now that this is a public API killing the q argument and
> just using req->q would make the API easier to understand.

Oh, my missing kerneldoc is clearly a problem. We need a separate
argument for the request_queue because the q we want to count stats for
may not be the one providing the request. For nvme multipath, we want to
count stats against the head's request_queue, but the request comes from
the ns path, so we need both args.

Re: [PATCHv2 1/2] block: export passthrough stats enabled

[Christoph Hellwig]

On Wed, May 27, 2026 at 07:22:11AM -0600, Keith Busch wrote:
> On Wed, May 27, 2026 at 03:14:58PM +0200, Christoph Hellwig wrote:
> > > +static inline bool blk_rq_passthrough_stats(struct request *req,
> > > +					    struct request_queue *q)
> > 
> > The kerneldoc requested last time would be really nice to have.
> > Also, now that this is a public API killing the q argument and
> > just using req->q would make the API easier to understand.
> 
> Oh, my missing kerneldoc is clearly a problem. We need a separate
> argument for the request_queue because the q we want to count stats for
> may not be the one providing the request.

Even more argument for having the documentation :)

[PATCHv2 2/2] nvme: add support multipath passthrough iostats

[Keith Busch]

From: Keith Busch <kbusch@kernel.org>

Don't skip io accounting for passthrough commands if the user enabled
tracking these.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/nvme/host/ioctl.c     | 4 ++++
 drivers/nvme/host/multipath.c | 5 ++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index 08889b20e5d8c..38ca04567406a 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -102,8 +102,12 @@ static struct request *nvme_alloc_user_request(struct request_queue *q,
 		struct nvme_command *cmd, blk_opf_t rq_flags,
 		blk_mq_req_flags_t blk_flags)
 {
+	struct nvme_ns *ns = q->queuedata;
 	struct request *req;
 
+	if (ns && nvme_ns_head_multipath(ns->head))
+		rq_flags |= REQ_NVME_MPATH;
+
 	req = blk_mq_alloc_request(q, nvme_req_op(cmd) | rq_flags, blk_flags);
 	if (IS_ERR(req))
 		return req;
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 263161cb8ac06..d0a95cde181c4 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -175,9 +175,12 @@ void nvme_mpath_start_request(struct request *rq)
 		nvme_req(rq)->flags |= NVME_MPATH_CNT_ACTIVE;
 	}
 
-	if (!blk_queue_io_stat(disk->queue) || blk_rq_is_passthrough(rq) ||
+	if (!blk_queue_io_stat(disk->queue) ||
 	    (nvme_req(rq)->flags & NVME_MPATH_IO_STATS))
 		return;
+	if (blk_rq_is_passthrough(rq) &&
+	    !blk_rq_passthrough_stats(rq, disk->queue))
+		return;
 
 	nvme_req(rq)->flags |= NVME_MPATH_IO_STATS;
 	nvme_req(rq)->start_time = bdev_start_io_acct(disk->part0, req_op(rq),
-- 
2.53.0-Meta

Re: [PATCHv2 2/2] nvme: add support multipath passthrough iostats

[Nilay Shroff]

On 5/26/26 9:09 PM, Keith Busch wrote:
> From: Keith Busch<kbusch@kernel.org>
> 
> Don't skip io accounting for passthrough commands if the user enabled
> tracking these.
> 
> Signed-off-by: Keith Busch<kbusch@kernel.org>
> ---
>   drivers/nvme/host/ioctl.c     | 4 ++++
>   drivers/nvme/host/multipath.c | 5 ++++-
>   2 files changed, 8 insertions(+), 1 deletion(-)

Looks good to me.
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>

Re: [PATCHv2 2/2] nvme: add support multipath passthrough iostats

[Nitesh Shetty]

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On 26/05/26 08:39AM, Keith Busch wrote:
>From: Keith Busch <kbusch@kernel.org>
>
>Don't skip io accounting for passthrough commands if the user enabled
>tracking these.
>
>Signed-off-by: Keith Busch <kbusch@kernel.org>
>---

Reviewed-by: Nitesh Shetty <nj.shetty@samsung.com>

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Re: [PATCHv2 2/2] nvme: add support multipath passthrough iostats

[Christoph Hellwig]

On Tue, May 26, 2026 at 08:39:21AM -0700, Keith Busch wrote:
> +	struct nvme_ns *ns = q->queuedata;
>  	struct request *req;
>  
> +	if (ns && nvme_ns_head_multipath(ns->head))
> +		rq_flags |= REQ_NVME_MPATH;

I just wanted to come with reasons why it this is wrong, but it actually
seems already - we only have a ns for multipath nodes if multipathing
is enabled.  Maybe throw a little comment in on that?

Otherwise looks good.

Re: [PATCHv2 2/2] nvme: add support multipath passthrough iostats

[Keith Busch]

On Wed, May 27, 2026 at 03:16:57PM +0200, Christoph Hellwig wrote:
> On Tue, May 26, 2026 at 08:39:21AM -0700, Keith Busch wrote:
> > +	struct nvme_ns *ns = q->queuedata;
> >  	struct request *req;
> >  
> > +	if (ns && nvme_ns_head_multipath(ns->head))
> > +		rq_flags |= REQ_NVME_MPATH;
> 
> I just wanted to come with reasons why it this is wrong, but it actually
> seems already - we only have a ns for multipath nodes if multipathing
> is enabled.  Maybe throw a little comment in on that?

Yes. An added subtlety here is that we unconditionally set
REQ_FAILFAST_DRIVER for passthrough requests, so it does not get
failover consideration. You can't steal bio's from a REQ_DRV_IN/OUT
request because all the necessary driver info is attached to the
original request, which doesn't follow the bio.