[PATCH v3 09/17] scsi-multipath: add scsi_mpath_{start,end}_request()

Add scsi_mpath_{start,end}_request() to handle updating private multipath
request data, like nvme_mpath_{start,end}_request().

New member Scsi_Host.mpath_nr_active is added. This is required for queue
depth multipath iopolicy.

For NVMe, this count is per controller. The reason is that many NSes may
be connected to a controller, so congestion should be judged at
controller level.

SCSI has no definition of a controller, but SCSI host is a comparable
concept.

Indeed, many SCSI disks may be connected to the same SCSI host, so it
makes sense to count number of active requests at this point. However,
for a transport like iSCSI Initiator over TCP/IP, we have a separate SCSI
host per SCSI device (so there the count would be same at SCSI device
level).


Signed-off-by: John Garry <[email protected]>
---
 drivers/scsi/scsi_lib.c       |  6 +++++
 drivers/scsi/scsi_multipath.c | 51 +++++++++++++++++++++++++++++++++++
 include/scsi/scsi_cmnd.h      |  5 ++++
 include/scsi/scsi_host.h      |  4 +++
 include/scsi/scsi_multipath.h |  8 ++++++
 5 files changed, 74 insertions(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index cc34253c467a2..f8b389fda2537 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -669,6 +669,9 @@ static bool scsi_end_request(struct request *req, blk_status_t error,
 	struct scsi_device *sdev = cmd->device;
 	struct request_queue *q = sdev->request_queue;
 
+	if (is_mpath_request(req))
+		scsi_mpath_end_request(req);
+
 	if (blk_update_request(req, error, bytes))
 		return true;
 
@@ -1917,6 +1920,9 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
 	memset(cmd->sense_buffer, 0, SCSI_SENSE_BUFFERSIZE);
 	cmd->submitter = SUBMITTED_BY_BLOCK_LAYER;
 
+	if (is_mpath_request(req))
+		scsi_mpath_start_request(req);
+
 	blk_mq_start_request(req);
 	if (blk_mq_is_reserved_rq(req)) {
 		reason = shost->hostt->queue_reserved_command(shost, cmd);
diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
index d8ea9ffe8942c..61fa2e4cdfdab 100644
--- a/drivers/scsi/scsi_multipath.c
+++ b/drivers/scsi/scsi_multipath.c
@@ -543,6 +543,57 @@ void scsi_mpath_put_head(struct scsi_mpath_head *scsi_mpath_head)
 }
 EXPORT_SYMBOL_GPL(scsi_mpath_put_head);
 
+void scsi_mpath_start_request(struct request *req)
+{
+	struct scsi_cmnd *scmd = blk_mq_rq_to_pdu(req);
+	struct scsi_device *sdev = scmd->device;
+	struct scsi_mpath_device *scsi_mpath_dev = sdev->scsi_mpath_dev;
+	struct scsi_mpath_head *scsi_mpath_head =
+				scsi_mpath_dev->scsi_mpath_head;
+	struct mpath_head *mpath_head = &scsi_mpath_head->mpath_head;
+	struct gendisk *disk = mpath_head->disk;
+
+	if (mpath_qd_iopolicy(&scsi_mpath_head->iopolicy) &&
+	    !(scmd->flags & SCMD_MPATH_CNT_ACTIVE)) {
+		struct Scsi_Host *shost = sdev->host;
+
+		atomic_inc(&shost->mpath_nr_active);
+		scmd->flags |= SCMD_MPATH_CNT_ACTIVE;
+	}
+
+	if (!blk_queue_io_stat(disk->queue) || blk_rq_is_passthrough(req) ||
+	    (scmd->flags & SCMD_MPATH_IO_STATS))
+		return;
+
+	scmd->flags |= SCMD_MPATH_IO_STATS;
+	scmd->start_time = bdev_start_io_acct(disk->part0, req_op(req),
+				jiffies);
+}
+
+void scsi_mpath_end_request(struct request *req)
+{
+	struct scsi_cmnd *scmd = blk_mq_rq_to_pdu(req);
+	struct scsi_device *sdev = scmd->device;
+	struct scsi_mpath_device *scsi_mpath_dev =
+			sdev->scsi_mpath_dev;
+	struct scsi_mpath_head *scsi_mpath_head =
+			scsi_mpath_dev->scsi_mpath_head;
+	struct mpath_head *mpath_head = &scsi_mpath_head->mpath_head;
+	struct gendisk *disk = mpath_head->disk;
+
+	if (scmd->flags & SCMD_MPATH_CNT_ACTIVE) {
+		struct Scsi_Host *shost = sdev->host;
+
+		atomic_dec_if_positive(&shost->mpath_nr_active);
+	}
+
+	if (!(scmd->flags & SCMD_MPATH_IO_STATS))
+		return;
+	bdev_end_io_acct(disk->part0, req_op(req),
+			 blk_rq_bytes(req) >> SECTOR_SHIFT,
+			 scmd->start_time);
+}
+
 int __init scsi_multipath_init(void)
 {
 	return class_register(&scsi_mpath_device_class);
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index 8ecfb94049db5..c6571a36e577b 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -60,6 +60,8 @@ struct scsi_pointer {
 #define SCMD_FAIL_IF_RECOVERING	(1 << 4)
 /* flags preserved across unprep / reprep */
 #define SCMD_PRESERVED_FLAGS	(SCMD_INITIALIZED | SCMD_FAIL_IF_RECOVERING)
+#define SCMD_MPATH_IO_STATS	(1 << 5)
+#define SCMD_MPATH_CNT_ACTIVE	(1 << 6)
 
 /* for scmd->state */
 #define SCMD_STATE_COMPLETE	0
@@ -139,6 +141,9 @@ struct scsi_cmnd {
 					 * to release this memory.  (The memory
 					 * obtained by scsi_malloc is guaranteed
 					 * to be at an address < 16Mb). */
+	#ifdef CONFIG_SCSI_MULTIPATH
+	unsigned long		start_time;
+	#endif
 
 	int result;		/* Status code from lower level driver */
 };
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 7e2011830ba4b..cf4fff3ea1a8e 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -753,6 +753,10 @@ struct Scsi_Host {
 	/* Delay for runtime autosuspend */
 	int rpm_autosuspend_delay;
 
+	#ifdef CONFIG_SCSI_MULTIPATH
+	atomic_t mpath_nr_active;
+	#endif
+
 	/*
 	 * We should ensure that this is aligned, both for better performance
 	 * and also because some compilers (m68k) don't automatically force
diff --git a/include/scsi/scsi_multipath.h b/include/scsi/scsi_multipath.h
index d8644d6261992..ed5c77d568843 100644
--- a/include/scsi/scsi_multipath.h
+++ b/include/scsi/scsi_multipath.h
@@ -55,6 +55,8 @@ void scsi_mpath_add_sysfs_link(struct scsi_device *sdev);
 void scsi_mpath_remove_sysfs_link(struct scsi_device *sdev);
 int scsi_mpath_get_head(struct scsi_mpath_head *scsi_mpath_head);
 void scsi_mpath_put_head(struct scsi_mpath_head *scsi_mpath_head);
+void scsi_mpath_start_request(struct request *req);
+void scsi_mpath_end_request(struct request *req);
 #else /* CONFIG_SCSI_MULTIPATH */
 
 struct scsi_mpath_head {
@@ -93,6 +95,12 @@ static inline
 void scsi_mpath_put_head(struct scsi_mpath_head *scsi_mpath_head)
 {
 }
+static inline void scsi_mpath_start_request(struct request *req)
+{
+}
+static inline void scsi_mpath_end_request(struct request *req)
+{
+}
 static inline void scsi_mpath_add_sysfs_link(struct scsi_device *sdev)
 {
 }
-- 
2.43.7