more BLK_MQ_F_* simplification

more BLK_MQ_F_* simplification

[Christoph Hellwig]

Hi Jens,

this series removes another BLK_MQ_F_ that just duplicates an implicit
condition and cleans up the tag allocation policy selection by using
an actual BLK_MQ_F_ flag instead of a two-value enum awkwardly encoded
into it.  If we'd ever grow another policy we'd be much better off just
adding a separate field to the tagset for it.

Diffstat:
 block/blk-mq-debugfs.c                 |   26 +++-----------------
 block/blk-mq-tag.c                     |   41 ++++++++++-----------------------
 block/blk-mq.c                         |    3 --
 block/blk-mq.h                         |    5 ----
 block/bsg-lib.c                        |    2 -
 block/elevator.c                       |   20 ----------------
 block/genhd.c                          |   28 ++++++++++++----------
 drivers/ata/ahci.h                     |    2 -
 drivers/ata/pata_macio.c               |    2 -
 drivers/ata/sata_mv.c                  |    2 -
 drivers/ata/sata_nv.c                  |    4 +--
 drivers/ata/sata_sil24.c               |    2 -
 drivers/block/null_blk/main.c          |    4 +--
 drivers/nvme/host/apple.c              |    1 
 drivers/nvme/host/core.c               |    1 
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c |    2 -
 drivers/scsi/scsi_lib.c                |    4 +--
 drivers/ufs/core/ufshcd.c              |    1 
 include/linux/blk-mq.h                 |   24 +++++--------------
 include/linux/libata.h                 |    4 +--
 include/scsi/scsi_host.h               |    7 ++++-
 21 files changed, 61 insertions(+), 124 deletions(-)

[PATCH 1/4] block: better split mq vs non-mq code in add_disk_fwnode

[Christoph Hellwig]

Add a big conditional for blk-mq vs not mq at the beginning of
add_disk_fwnode so that elevator_init_mq is only called for blk-mq disks,
and add checks that the right methods or set or not set based on the
queue type.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/genhd.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 5678194b6b1a..018721b14053 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -400,21 +400,23 @@ int __must_check add_disk_fwnode(struct device *parent, struct gendisk *disk,
 	struct device *ddev = disk_to_dev(disk);
 	int ret;
 
-	/* Only makes sense for bio-based to set ->poll_bio */
-	if (queue_is_mq(disk->queue) && disk->fops->poll_bio)
-		return -EINVAL;
-
-	/*
-	 * The disk queue should now be all set with enough information about
-	 * the device for the elevator code to pick an adequate default
-	 * elevator if one is needed, that is, for devices requesting queue
-	 * registration.
-	 */
-	elevator_init_mq(disk->queue);
+	if (queue_is_mq(disk->queue)) {
+		/*
+		 * ->submit_bio and ->poll_bio are bypassed for blk-mq drivers.
+		 */
+		if (disk->fops->submit_bio || disk->fops->poll_bio)
+			return -EINVAL;
 
-	/* Mark bdev as having a submit_bio, if needed */
-	if (disk->fops->submit_bio)
+		/*
+		 * Initialize the I/O scheduler code and pick a default one if
+		 * needed.
+		 */
+		elevator_init_mq(disk->queue);
+	} else {
+		if (!disk->fops->submit_bio)
+			return -EINVAL;
 		bdev_set_flag(disk->part0, BD_HAS_SUBMIT_BIO);
+	}
 
 	/*
 	 * If the driver provides an explicit major number it also must provide
-- 
2.45.2

[PATCH 2/4] block: remove blk_mq_init_bitmaps

[Christoph Hellwig]

The little work done in blk_mq_init_bitmaps is easier done in the only
caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq-tag.c | 38 ++++++++++++--------------------------
 block/blk-mq.h     |  3 ---
 2 files changed, 12 insertions(+), 29 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 2cafcf11ee8b..ab4a66791a20 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -544,30 +544,12 @@ static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
 				       node);
 }
 
-int blk_mq_init_bitmaps(struct sbitmap_queue *bitmap_tags,
-			struct sbitmap_queue *breserved_tags,
-			unsigned int queue_depth, unsigned int reserved,
-			int node, int alloc_policy)
-{
-	unsigned int depth = queue_depth - reserved;
-	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
-
-	if (bt_alloc(bitmap_tags, depth, round_robin, node))
-		return -ENOMEM;
-	if (bt_alloc(breserved_tags, reserved, round_robin, node))
-		goto free_bitmap_tags;
-
-	return 0;
-
-free_bitmap_tags:
-	sbitmap_queue_free(bitmap_tags);
-	return -ENOMEM;
-}
-
 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 				     unsigned int reserved_tags,
 				     int node, int alloc_policy)
 {
+	unsigned int depth = total_tags - reserved_tags;
+	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
 	struct blk_mq_tags *tags;
 
 	if (total_tags > BLK_MQ_TAG_MAX) {
@@ -582,14 +564,18 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 	tags->nr_tags = total_tags;
 	tags->nr_reserved_tags = reserved_tags;
 	spin_lock_init(&tags->lock);
+	if (bt_alloc(&tags->bitmap_tags, depth, round_robin, node))
+		goto out_free_tags;
+	if (bt_alloc(&tags->breserved_tags, reserved_tags, round_robin, node))
+		goto out_free_bitmap_tags;
 
-	if (blk_mq_init_bitmaps(&tags->bitmap_tags, &tags->breserved_tags,
-				total_tags, reserved_tags, node,
-				alloc_policy) < 0) {
-		kfree(tags);
-		return NULL;
-	}
 	return tags;
+
+out_free_bitmap_tags:
+	sbitmap_queue_free(&tags->bitmap_tags);
+out_free_tags:
+	kfree(tags);
+	return NULL;
 }
 
 void blk_mq_free_tags(struct blk_mq_tags *tags)
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 89a20fffa4b1..3bb9ea80f9b6 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -165,9 +165,6 @@ struct blk_mq_alloc_data {
 struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags,
 		unsigned int reserved_tags, int node, int alloc_policy);
 void blk_mq_free_tags(struct blk_mq_tags *tags);
-int blk_mq_init_bitmaps(struct sbitmap_queue *bitmap_tags,
-		struct sbitmap_queue *breserved_tags, unsigned int queue_depth,
-		unsigned int reserved, int node, int alloc_policy);
 
 unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
 unsigned long blk_mq_get_tags(struct blk_mq_alloc_data *data, int nr_tags,
-- 
2.45.2

Re: [PATCH 2/4] block: remove blk_mq_init_bitmaps

[John Garry]

On 03/01/2025 07:42, Christoph Hellwig wrote:
> The little work done in blk_mq_init_bitmaps is easier done in the only
> caller.
> 
> Signed-off-by: Christoph Hellwig<hch@lst.de>

Reviewed-by: John Garry <john.g.garry@oracle.com>

[PATCH 3/4] block: remove BLK_MQ_F_NO_SCHED

[Christoph Hellwig]

The only queues that really can't support a scheduler are those that
do not have a gendisk associated with them, and thus can't be used for
non-passthrough commands.  In addition to those null_blk can optionally
set the flag, which is a bad odd.  Replace the null_blk usage with
BLK_MQ_F_NO_SCHED_BY_DEFAULT to keep the expected semantics and then
remove BLK_MQ_F_NO_SCHED as the non-disk queues never call into
elevator_init_mq or blk_register_queue which adds the sysfs attributes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq-debugfs.c        |  1 -
 block/bsg-lib.c               |  2 +-
 block/elevator.c              | 20 --------------------
 drivers/block/null_blk/main.c |  4 ++--
 drivers/nvme/host/apple.c     |  1 -
 drivers/nvme/host/core.c      |  1 -
 drivers/ufs/core/ufshcd.c     |  1 -
 include/linux/blk-mq.h        |  2 --
 8 files changed, 3 insertions(+), 29 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 4b6b20ccdb53..64b3c333aa47 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -185,7 +185,6 @@ static const char *const hctx_flag_name[] = {
 	HCTX_FLAG_NAME(STACKING),
 	HCTX_FLAG_NAME(TAG_HCTX_SHARED),
 	HCTX_FLAG_NAME(BLOCKING),
-	HCTX_FLAG_NAME(NO_SCHED),
 	HCTX_FLAG_NAME(NO_SCHED_BY_DEFAULT),
 };
 #undef HCTX_FLAG_NAME
diff --git a/block/bsg-lib.c b/block/bsg-lib.c
index 32da4a4429ce..93523d8f8195 100644
--- a/block/bsg-lib.c
+++ b/block/bsg-lib.c
@@ -381,7 +381,7 @@ struct request_queue *bsg_setup_queue(struct device *dev, const char *name,
 	set->queue_depth = 128;
 	set->numa_node = NUMA_NO_NODE;
 	set->cmd_size = sizeof(struct bsg_job) + dd_job_size;
-	set->flags = BLK_MQ_F_NO_SCHED | BLK_MQ_F_BLOCKING;
+	set->flags = BLK_MQ_F_BLOCKING;
 	if (blk_mq_alloc_tag_set(set))
 		goto out_tag_set;
 
diff --git a/block/elevator.c b/block/elevator.c
index be6e994256ac..b81216c48b6b 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -547,14 +547,6 @@ void elv_unregister(struct elevator_type *e)
 }
 EXPORT_SYMBOL_GPL(elv_unregister);
 
-static inline bool elv_support_iosched(struct request_queue *q)
-{
-	if (!queue_is_mq(q) ||
-	    (q->tag_set->flags & BLK_MQ_F_NO_SCHED))
-		return false;
-	return true;
-}
-
 /*
  * For single queue devices, default to using mq-deadline. If we have multiple
  * queues or mq-deadline is not available, default to "none".
@@ -580,9 +572,6 @@ void elevator_init_mq(struct request_queue *q)
 	struct elevator_type *e;
 	int err;
 
-	if (!elv_support_iosched(q))
-		return;
-
 	WARN_ON_ONCE(blk_queue_registered(q));
 
 	if (unlikely(q->elevator))
@@ -714,9 +703,6 @@ void elv_iosched_load_module(struct gendisk *disk, const char *buf,
 	struct elevator_type *found;
 	const char *name;
 
-	if (!elv_support_iosched(disk->queue))
-		return;
-
 	strscpy(elevator_name, buf, sizeof(elevator_name));
 	name = strstrip(elevator_name);
 
@@ -734,9 +720,6 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf,
 	char elevator_name[ELV_NAME_MAX];
 	int ret;
 
-	if (!elv_support_iosched(disk->queue))
-		return count;
-
 	strscpy(elevator_name, buf, sizeof(elevator_name));
 	ret = elevator_change(disk->queue, strstrip(elevator_name));
 	if (!ret)
@@ -751,9 +734,6 @@ ssize_t elv_iosched_show(struct gendisk *disk, char *name)
 	struct elevator_type *cur = NULL, *e;
 	int len = 0;
 
-	if (!elv_support_iosched(q))
-		return sprintf(name, "none\n");
-
 	if (!q->elevator) {
 		len += sprintf(name+len, "[none] ");
 	} else {
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 178e62cd9a9f..d94ef37480bd 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1792,7 +1792,7 @@ static int null_init_global_tag_set(void)
 	tag_set.queue_depth = g_hw_queue_depth;
 	tag_set.numa_node = g_home_node;
 	if (g_no_sched)
-		tag_set.flags |= BLK_MQ_F_NO_SCHED;
+		tag_set.flags |= BLK_MQ_F_NO_SCHED_BY_DEFAULT;
 	if (g_shared_tag_bitmap)
 		tag_set.flags |= BLK_MQ_F_TAG_HCTX_SHARED;
 	if (g_blocking)
@@ -1817,7 +1817,7 @@ static int null_setup_tagset(struct nullb *nullb)
 	nullb->tag_set->queue_depth = nullb->dev->hw_queue_depth;
 	nullb->tag_set->numa_node = nullb->dev->home_node;
 	if (nullb->dev->no_sched)
-		nullb->tag_set->flags |= BLK_MQ_F_NO_SCHED;
+		nullb->tag_set->flags |= BLK_MQ_F_NO_SCHED_BY_DEFAULT;
 	if (nullb->dev->shared_tag_bitmap)
 		nullb->tag_set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
 	if (nullb->dev->blocking)
diff --git a/drivers/nvme/host/apple.c b/drivers/nvme/host/apple.c
index 83c60468542c..1de11b722f04 100644
--- a/drivers/nvme/host/apple.c
+++ b/drivers/nvme/host/apple.c
@@ -1251,7 +1251,6 @@ static int apple_nvme_alloc_tagsets(struct apple_nvme *anv)
 	anv->admin_tagset.timeout = NVME_ADMIN_TIMEOUT;
 	anv->admin_tagset.numa_node = NUMA_NO_NODE;
 	anv->admin_tagset.cmd_size = sizeof(struct apple_nvme_iod);
-	anv->admin_tagset.flags = BLK_MQ_F_NO_SCHED;
 	anv->admin_tagset.driver_data = &anv->adminq;
 
 	ret = blk_mq_alloc_tag_set(&anv->admin_tagset);
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 42283d268500..c2250ddef5a2 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4564,7 +4564,6 @@ int nvme_alloc_admin_tag_set(struct nvme_ctrl *ctrl, struct blk_mq_tag_set *set,
 		/* Reserved for fabric connect and keep alive */
 		set->reserved_tags = 2;
 	set->numa_node = ctrl->numa_node;
-	set->flags = BLK_MQ_F_NO_SCHED;
 	if (ctrl->ops->flags & NVME_F_BLOCKING)
 		set->flags |= BLK_MQ_F_BLOCKING;
 	set->cmd_size = cmd_size;
diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 8a01e4393159..fd53c9f402c3 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -10412,7 +10412,6 @@ static int ufshcd_add_scsi_host(struct ufs_hba *hba)
 		.nr_hw_queues	= 1,
 		.queue_depth	= hba->nutmrs,
 		.ops		= &ufshcd_tmf_ops,
-		.flags		= BLK_MQ_F_NO_SCHED,
 	};
 	err = blk_mq_alloc_tag_set(&hba->tmf_tag_set);
 	if (err < 0)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 6340293511c9..f2ff0ffa0535 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -676,8 +676,6 @@ enum {
 	BLK_MQ_F_STACKING	= 1 << 2,
 	BLK_MQ_F_TAG_HCTX_SHARED = 1 << 3,
 	BLK_MQ_F_BLOCKING	= 1 << 4,
-	/* Do not allow an I/O scheduler to be configured. */
-	BLK_MQ_F_NO_SCHED	= 1 << 5,
 
 	/*
 	 * Select 'none' during queue registration in case of a single hwq
-- 
2.45.2

[PATCH 4/4] block: simplify tag allocation policy selection

[Christoph Hellwig]

Use a plain BLK_MQ_F_* flag to select the round robin tag selection
instead of overlaying an enum with just two possible values into the
flags space.  Keep the value based selection inside of SCSI as the
BLK_MQ_F_ flags aren't directly exposed to SCSI LLDDs.

Doing so allows adding a BLK_MQ_F_MAX sentinel for simplified overflow
checking in the messy debugfs helpers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq-debugfs.c                 | 25 ++++---------------------
 block/blk-mq-tag.c                     |  5 ++---
 block/blk-mq.c                         |  3 +--
 block/blk-mq.h                         |  2 +-
 drivers/ata/ahci.h                     |  2 +-
 drivers/ata/pata_macio.c               |  2 +-
 drivers/ata/sata_mv.c                  |  2 +-
 drivers/ata/sata_nv.c                  |  4 ++--
 drivers/ata/sata_sil24.c               |  2 +-
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c |  2 +-
 drivers/scsi/scsi_lib.c                |  4 ++--
 include/linux/blk-mq.h                 | 22 +++++++---------------
 include/linux/libata.h                 |  4 ++--
 include/scsi/scsi_host.h               |  7 ++++++-
 14 files changed, 32 insertions(+), 54 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 64b3c333aa47..adf5f0697b6b 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -172,19 +172,13 @@ static int hctx_state_show(void *data, struct seq_file *m)
 	return 0;
 }
 
-#define BLK_TAG_ALLOC_NAME(name) [BLK_TAG_ALLOC_##name] = #name
-static const char *const alloc_policy_name[] = {
-	BLK_TAG_ALLOC_NAME(FIFO),
-	BLK_TAG_ALLOC_NAME(RR),
-};
-#undef BLK_TAG_ALLOC_NAME
-
 #define HCTX_FLAG_NAME(name) [ilog2(BLK_MQ_F_##name)] = #name
 static const char *const hctx_flag_name[] = {
 	HCTX_FLAG_NAME(TAG_QUEUE_SHARED),
 	HCTX_FLAG_NAME(STACKING),
 	HCTX_FLAG_NAME(TAG_HCTX_SHARED),
 	HCTX_FLAG_NAME(BLOCKING),
+	HCTX_FLAG_NAME(TAG_RR),
 	HCTX_FLAG_NAME(NO_SCHED_BY_DEFAULT),
 };
 #undef HCTX_FLAG_NAME
@@ -192,22 +186,11 @@ static const char *const hctx_flag_name[] = {
 static int hctx_flags_show(void *data, struct seq_file *m)
 {
 	struct blk_mq_hw_ctx *hctx = data;
-	const int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(hctx->flags);
 
-	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) !=
-			BLK_MQ_F_ALLOC_POLICY_START_BIT);
-	BUILD_BUG_ON(ARRAY_SIZE(alloc_policy_name) != BLK_TAG_ALLOC_MAX);
+	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) != ilog2(BLK_MQ_F_MAX));
 
-	seq_puts(m, "alloc_policy=");
-	if (alloc_policy < ARRAY_SIZE(alloc_policy_name) &&
-	    alloc_policy_name[alloc_policy])
-		seq_puts(m, alloc_policy_name[alloc_policy]);
-	else
-		seq_printf(m, "%d", alloc_policy);
-	seq_puts(m, " ");
-	blk_flags_show(m,
-		       hctx->flags ^ BLK_ALLOC_POLICY_TO_MQ_FLAG(alloc_policy),
-		       hctx_flag_name, ARRAY_SIZE(hctx_flag_name));
+	blk_flags_show(m, hctx->flags, hctx_flag_name,
+			ARRAY_SIZE(hctx_flag_name));
 	seq_puts(m, "\n");
 	return 0;
 }
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index ab4a66791a20..b9f417d980b4 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -545,11 +545,10 @@ static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
 }
 
 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
-				     unsigned int reserved_tags,
-				     int node, int alloc_policy)
+		unsigned int reserved_tags, unsigned int flags, int node)
 {
 	unsigned int depth = total_tags - reserved_tags;
-	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
+	bool round_robin = flags & BLK_MQ_F_TAG_RR;
 	struct blk_mq_tags *tags;
 
 	if (total_tags > BLK_MQ_TAG_MAX) {
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 17f10683d640..2e6132f778fd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3476,8 +3476,7 @@ static struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
 	if (node == NUMA_NO_NODE)
 		node = set->numa_node;
 
-	tags = blk_mq_init_tags(nr_tags, reserved_tags, node,
-				BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
+	tags = blk_mq_init_tags(nr_tags, reserved_tags, set->flags, node);
 	if (!tags)
 		return NULL;
 
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 3bb9ea80f9b6..c872bbbe6411 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -163,7 +163,7 @@ struct blk_mq_alloc_data {
 };
 
 struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags,
-		unsigned int reserved_tags, int node, int alloc_policy);
+		unsigned int reserved_tags, unsigned int flags, int node);
 void blk_mq_free_tags(struct blk_mq_tags *tags);
 
 unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
index 8f40f75ba08c..64ce2f83feaa 100644
--- a/drivers/ata/ahci.h
+++ b/drivers/ata/ahci.h
@@ -396,7 +396,7 @@ extern const struct attribute_group *ahci_sdev_groups[];
 	.shost_groups		= ahci_shost_groups,			\
 	.sdev_groups		= ahci_sdev_groups,			\
 	.change_queue_depth     = ata_scsi_change_queue_depth,		\
-	.tag_alloc_policy       = BLK_TAG_ALLOC_RR,             	\
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,			\
 	.device_configure	= ata_scsi_device_configure
 
 extern struct ata_port_operations ahci_ops;
diff --git a/drivers/ata/pata_macio.c b/drivers/ata/pata_macio.c
index f2f36e55a1f4..5a3ee6417b57 100644
--- a/drivers/ata/pata_macio.c
+++ b/drivers/ata/pata_macio.c
@@ -935,7 +935,7 @@ static const struct scsi_host_template pata_macio_sht = {
 	.device_configure	= pata_macio_device_configure,
 	.sdev_groups		= ata_common_sdev_groups,
 	.can_queue		= ATA_DEF_QUEUE,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,
 };
 
 static struct ata_port_operations pata_macio_ops = {
diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
index b8f363370e1a..fb70c8cf233c 100644
--- a/drivers/ata/sata_mv.c
+++ b/drivers/ata/sata_mv.c
@@ -672,7 +672,7 @@ static const struct scsi_host_template mv6_sht = {
 	.dma_boundary		= MV_DMA_BOUNDARY,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth	= ata_scsi_change_queue_depth,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,
 	.device_configure	= ata_scsi_device_configure
 };
 
diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
index 36d99043ef50..56bc598c8f72 100644
--- a/drivers/ata/sata_nv.c
+++ b/drivers/ata/sata_nv.c
@@ -385,7 +385,7 @@ static const struct scsi_host_template nv_adma_sht = {
 	.device_configure	= nv_adma_device_configure,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth     = ata_scsi_change_queue_depth,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,
 };
 
 static const struct scsi_host_template nv_swncq_sht = {
@@ -396,7 +396,7 @@ static const struct scsi_host_template nv_swncq_sht = {
 	.device_configure	= nv_swncq_device_configure,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth     = ata_scsi_change_queue_depth,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,
 };
 
 /*
diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index 72c03cbdaff4..d51eeba4da3c 100644
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -378,7 +378,7 @@ static const struct scsi_host_template sil24_sht = {
 	.can_queue		= SIL24_MAX_CMDS,
 	.sg_tablesize		= SIL24_MAX_SGE,
 	.dma_boundary		= ATA_DMA_BOUNDARY,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_FIFO,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth	= ata_scsi_change_queue_depth,
 	.device_configure	= ata_scsi_device_configure
diff --git a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
index 79129c977704..cb23d2d3b29f 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
@@ -3345,7 +3345,7 @@ static const struct scsi_host_template sht_v3_hw = {
 	.slave_alloc		= hisi_sas_slave_alloc,
 	.shost_groups		= host_v3_hw_groups,
 	.sdev_groups		= sdev_groups_v3_hw,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,
 	.host_reset             = hisi_sas_host_reset,
 	.host_tagset		= 1,
 	.mq_poll		= queue_complete_v3_hw,
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 5cf124e13097..94869a0e4ba4 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2065,8 +2065,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 	tag_set->queue_depth = shost->can_queue;
 	tag_set->cmd_size = cmd_size;
 	tag_set->numa_node = dev_to_node(shost->dma_dev);
-	tag_set->flags |=
-		BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
+	if (shost->hostt->tag_alloc_policy == SCSI_TAG_ALLOC_RR)
+		tag_set->flags |= BLK_MQ_F_TAG_RR;
 	if (shost->queuecommand_may_block)
 		tag_set->flags |= BLK_MQ_F_BLOCKING;
 	tag_set->driver_data = shost;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f2ff0ffa0535..a0a9007cc1e3 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -296,13 +296,6 @@ enum blk_eh_timer_return {
 	BLK_EH_RESET_TIMER,
 };
 
-/* Keep alloc_policy_name[] in sync with the definitions below */
-enum {
-	BLK_TAG_ALLOC_FIFO,	/* allocate starting from 0 */
-	BLK_TAG_ALLOC_RR,	/* allocate starting from last allocated tag */
-	BLK_TAG_ALLOC_MAX
-};
-
 /**
  * struct blk_mq_hw_ctx - State for a hardware queue facing the hardware
  * block device
@@ -677,20 +670,19 @@ enum {
 	BLK_MQ_F_TAG_HCTX_SHARED = 1 << 3,
 	BLK_MQ_F_BLOCKING	= 1 << 4,
 
+	/*
+	 * Alloc tags on a round-robin base instead of the first available one.
+	 */
+	BLK_MQ_F_TAG_RR		= 1 << 5,
+
 	/*
 	 * Select 'none' during queue registration in case of a single hwq
 	 * or shared hwqs instead of 'mq-deadline'.
 	 */
 	BLK_MQ_F_NO_SCHED_BY_DEFAULT	= 1 << 6,
-	BLK_MQ_F_ALLOC_POLICY_START_BIT = 7,
-	BLK_MQ_F_ALLOC_POLICY_BITS = 1,
+
+	BLK_MQ_F_MAX = 1 << 7,
 };
-#define BLK_MQ_FLAG_TO_ALLOC_POLICY(flags) \
-	((flags >> BLK_MQ_F_ALLOC_POLICY_START_BIT) & \
-		((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1))
-#define BLK_ALLOC_POLICY_TO_MQ_FLAG(policy) \
-	((policy & ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1)) \
-		<< BLK_MQ_F_ALLOC_POLICY_START_BIT)
 
 #define BLK_MQ_MAX_DEPTH	(10240)
 #define BLK_MQ_NO_HCTX_IDX	(-1U)
diff --git a/include/linux/libata.h b/include/linux/libata.h
index c1a85d46eba6..73a038ee0500 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -1467,13 +1467,13 @@ extern const struct attribute_group *ata_common_sdev_groups[];
 #define ATA_SUBBASE_SHT(drv_name)				\
 	__ATA_BASE_SHT(drv_name),				\
 	.can_queue		= ATA_DEF_QUEUE,		\
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,		\
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,		\
 	.device_configure	= ata_scsi_device_configure
 
 #define ATA_SUBBASE_SHT_QD(drv_name, drv_qd)			\
 	__ATA_BASE_SHT(drv_name),				\
 	.can_queue		= drv_qd,			\
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,		\
+	.tag_alloc_policy	= SCSI_TAG_ALLOC_RR,		\
 	.device_configure	= ata_scsi_device_configure
 
 #define ATA_BASE_SHT(drv_name)					\
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 2b4ab0369ffb..6163f2de4cbd 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -39,6 +39,11 @@ enum scsi_timeout_action {
 	SCSI_EH_NOT_HANDLED,
 };
 
+enum scsi_tag_alloc_policy {
+	SCSI_TAG_ALLOC_FIFO,	/* allocate starting from 0 */
+	SCSI_TAG_ALLOC_RR,	/* allocate starting from last allocated tag */
+};
+
 struct scsi_host_template {
 	/*
 	 * Put fields referenced in IO submission path together in
@@ -439,7 +444,7 @@ struct scsi_host_template {
 	short cmd_per_lun;
 
 	/* If use block layer to manage tags, this is tag allocation policy */
-	int tag_alloc_policy;
+	enum scsi_tag_alloc_policy tag_alloc_policy;
 
 	/*
 	 * Track QUEUE_FULL events and reduce queue depth on demand.
-- 
2.45.2

Re: [PATCH 4/4] block: simplify tag allocation policy selection

[John Garry]

>   };
>   #undef HCTX_FLAG_NAME
> @@ -192,22 +186,11 @@ static const char *const hctx_flag_name[] = {
>   static int hctx_flags_show(void *data, struct seq_file *m)
>   {
>   	struct blk_mq_hw_ctx *hctx = data;
> -	const int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(hctx->flags);
>   
> -	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) !=
> -			BLK_MQ_F_ALLOC_POLICY_START_BIT);
> -	BUILD_BUG_ON(ARRAY_SIZE(alloc_policy_name) != BLK_TAG_ALLOC_MAX);
> +	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) != ilog2(BLK_MQ_F_MAX));
>   
> -	seq_puts(m, "alloc_policy=");

Maybe it's nice to preserve this formatting, but I know that debugfs is 
not a stable ABI...

> -	if (alloc_policy < ARRAY_SIZE(alloc_policy_name) &&
> -	    alloc_policy_name[alloc_policy])
> -		seq_puts(m, alloc_policy_name[alloc_policy]);
> -	else
> -		seq_printf(m, "%d", alloc_policy);
> -	seq_puts(m, " ");
> -	blk_flags_show(m,
> -		       hctx->flags ^ BLK_ALLOC_POLICY_TO_MQ_FLAG(alloc_policy),
> -		       hctx_flag_name, ARRAY_SIZE(hctx_flag_name));
> +	blk_flags_show(m, hctx->flags, hctx_flag_name,
> +			ARRAY_SIZE(hctx_flag_name));
>   	seq_puts(m, "\n");
>   	return 0;



>   /*
> diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
> index 72c03cbdaff4..d51eeba4da3c 100644
> --- a/drivers/ata/sata_sil24.c
> +++ b/drivers/ata/sata_sil24.c
> @@ -378,7 +378,7 @@ static const struct scsi_host_template sil24_sht = {
>   	.can_queue		= SIL24_MAX_CMDS,
>   	.sg_tablesize		= SIL24_MAX_SGE,
>   	.dma_boundary		= ATA_DMA_BOUNDARY,
> -	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,
> +	.tag_alloc_policy	= SCSI_TAG_ALLOC_FIFO,

do we actually need to set tag_alloc_policy to the default 
(SCSI_TAG_ALLOC_FIFO)?

>   	.sdev_groups		= ata_ncq_sdev_groups,

> @@ -39,6 +39,11 @@ enum scsi_timeout_action {
>   	SCSI_EH_NOT_HANDLED,
>   };
>   
> +enum scsi_tag_alloc_policy {
> +	SCSI_TAG_ALLOC_FIFO,	/* allocate starting from 0 */
> +	SCSI_TAG_ALLOC_RR,	/* allocate starting from last allocated tag */
> +};


Could we just have

struct scsi_host_template {
	...
	int tag_alloc_policy_rr:1

instead of this enum?

Or does that cause issues for the ATA SHT and descendants where it 
overrides members? I didn't think that it would.

> +
>   struct scsi_host_template {
>   	/*
>   	 * Put fields referenced in IO submission path together in
> @@ -439,7 +444,7 @@ struct scsi_host_template {
>   	short cmd_per_lun;
>   
>   	/* If use block layer to manage tags, this is tag allocation policy */
> -	int tag_alloc_policy;
> +	enum scsi_tag_alloc_policy tag_alloc_policy;
>   
>   	/*
>   	 * Track QUEUE_FULL events and reduce queue depth on demand.

Re: [PATCH 4/4] block: simplify tag allocation policy selection

[Christoph Hellwig]

On Fri, Jan 03, 2025 at 09:33:31AM +0000, John Garry wrote:
>> -	BUILD_BUG_ON(ARRAY_SIZE(alloc_policy_name) != BLK_TAG_ALLOC_MAX);
>> +	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) != ilog2(BLK_MQ_F_MAX));
>>   -	seq_puts(m, "alloc_policy=");
>
> Maybe it's nice to preserve this formatting, but I know that debugfs is not 
> a stable ABI...

It's not a stable API indeed, and I'd rather not keep extra code for
debugging.

>> index 72c03cbdaff4..d51eeba4da3c 100644
>> --- a/drivers/ata/sata_sil24.c
>> +++ b/drivers/ata/sata_sil24.c
>> @@ -378,7 +378,7 @@ static const struct scsi_host_template sil24_sht = {
>>   	.can_queue		= SIL24_MAX_CMDS,
>>   	.sg_tablesize		= SIL24_MAX_SGE,
>>   	.dma_boundary		= ATA_DMA_BOUNDARY,
>> -	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,
>> +	.tag_alloc_policy	= SCSI_TAG_ALLOC_FIFO,
>
> do we actually need to set tag_alloc_policy to the default 
> (SCSI_TAG_ALLOC_FIFO)?

libata uses weird inheritance where __ATA_BASE_SHT sets default fields
that can then later be override, so this is indeed needed to set the
field back to the original default after the previous assignment changed
it.  (Did I mentioned I hate this style of programming? :))

> Could we just have
>
> struct scsi_host_template {
> 	...
> 	int tag_alloc_policy_rr:1
>
> instead of this enum?

This should probably work.  I tried to reduce the churn a bit, but
due to the change of the enum value names that didn't actually work.

>
> Or does that cause issues for the ATA SHT and descendants where it 
> overrides members? I didn't think that it would.

It'll still work fine.  It will be even less obvious, so the case
mentioned above by you will probably have to grow a comment explaining
it to preempt the cleanup brigade from removing it.

Re: [PATCH 4/4] block: simplify tag allocation policy selection

[Christoph Hellwig]

On Mon, Jan 06, 2025 at 08:35:20AM +0100, Christoph Hellwig wrote:
> >> --- a/drivers/ata/sata_sil24.c
> >> +++ b/drivers/ata/sata_sil24.c
> >> @@ -378,7 +378,7 @@ static const struct scsi_host_template sil24_sht = {
> >>   	.can_queue		= SIL24_MAX_CMDS,
> >>   	.sg_tablesize		= SIL24_MAX_SGE,
> >>   	.dma_boundary		= ATA_DMA_BOUNDARY,
> >> -	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,
> >> +	.tag_alloc_policy	= SCSI_TAG_ALLOC_FIFO,
> >
> > do we actually need to set tag_alloc_policy to the default 
> > (SCSI_TAG_ALLOC_FIFO)?
> 
> libata uses weird inheritance where __ATA_BASE_SHT sets default fields
> that can then later be override, so this is indeed needed to set the
> field back to the original default after the previous assignment changed
> it.  (Did I mentioned I hate this style of programming? :))

It turns out the clearning is not needed here, as the driver only
uses __ATA_BASE_SHT and not ATA_BASE_SHT (did I mentioned I hate this
templating?)

Re: [PATCH 4/4] block: simplify tag allocation policy selection

[John Garry]

On 06/01/2025 07:58, Christoph Hellwig wrote:
> On Mon, Jan 06, 2025 at 08:35:20AM +0100, Christoph Hellwig wrote:
>>>> --- a/drivers/ata/sata_sil24.c
>>>> +++ b/drivers/ata/sata_sil24.c
>>>> @@ -378,7 +378,7 @@ static const struct scsi_host_template sil24_sht = {
>>>>    	.can_queue		= SIL24_MAX_CMDS,
>>>>    	.sg_tablesize		= SIL24_MAX_SGE,
>>>>    	.dma_boundary		= ATA_DMA_BOUNDARY,
>>>> -	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,
>>>> +	.tag_alloc_policy	= SCSI_TAG_ALLOC_FIFO,
>>> do we actually need to set tag_alloc_policy to the default
>>> (SCSI_TAG_ALLOC_FIFO)?
>> libata uses weird inheritance where __ATA_BASE_SHT sets default fields
>> that can then later be override, so this is indeed needed to set the
>> field back to the original default after the previous assignment changed
>> it.  (Did I mentioned I hate this style of programming? :))
> It turns out the clearning is not needed here, as the driver only
> uses __ATA_BASE_SHT and not ATA_BASE_SHT 

Yeah, if you build with W=1, you get "initialized field overwritten" 
error when trying to set a value more than once in the structure.

(did I mentioned I hate this
> templating?

Sure, but it reduces lots of code. Maybe a nicer model is something like 
scsi_host_alloc(), which sets defaults (when not set).

)

more BLK_MQ_F_* simplification v2

[Christoph Hellwig]

Hi Jens,

this series removes another BLK_MQ_F_ that just duplicates an implicit
condition and cleans up the tag allocation policy selection by using
an actual BLK_MQ_F_ flag instead of a two-value enum awkwardly encoded
into it.  If we'd ever grow another policy we'd be much better off just
adding a separate field to the tagset for it.

Changes since v1:
 - use a boolean bitfield for the SCSI RR tag allocation policy selection

Diffstat:
 block/blk-mq-debugfs.c                 |   26 +++-----------------
 block/blk-mq-tag.c                     |   41 ++++++++++-----------------------
 block/blk-mq.c                         |    3 --
 block/blk-mq.h                         |    5 ----
 block/bsg-lib.c                        |    2 -
 block/elevator.c                       |   20 ----------------
 block/genhd.c                          |   28 ++++++++++++----------
 drivers/ata/ahci.h                     |    2 -
 drivers/ata/pata_macio.c               |    2 -
 drivers/ata/sata_mv.c                  |    2 -
 drivers/ata/sata_nv.c                  |    4 +--
 drivers/ata/sata_sil24.c               |    1 
 drivers/block/null_blk/main.c          |    4 +--
 drivers/nvme/host/apple.c              |    1 
 drivers/nvme/host/core.c               |    1 
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c |    2 -
 drivers/scsi/scsi_lib.c                |    4 +--
 drivers/ufs/core/ufshcd.c              |    1 
 include/linux/blk-mq.h                 |   24 +++++--------------
 include/linux/libata.h                 |    4 +--
 include/scsi/scsi_host.h               |    6 +++-
 21 files changed, 58 insertions(+), 125 deletions(-)

[PATCH 4/4] block: simplify tag allocation policy selection

[Christoph Hellwig]

Use a plain BLK_MQ_F_* flag to select the round robin tag selection
instead of overlaying an enum with just two possible values into the
flags space.

Doing so allows adding a BLK_MQ_F_MAX sentinel for simplified overflow
checking in the messy debugfs helpers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq-debugfs.c                 | 25 ++++---------------------
 block/blk-mq-tag.c                     |  5 ++---
 block/blk-mq.c                         |  3 +--
 block/blk-mq.h                         |  2 +-
 drivers/ata/ahci.h                     |  2 +-
 drivers/ata/pata_macio.c               |  2 +-
 drivers/ata/sata_mv.c                  |  2 +-
 drivers/ata/sata_nv.c                  |  4 ++--
 drivers/ata/sata_sil24.c               |  1 -
 drivers/scsi/hisi_sas/hisi_sas_v3_hw.c |  2 +-
 drivers/scsi/scsi_lib.c                |  4 ++--
 include/linux/blk-mq.h                 | 22 +++++++---------------
 include/linux/libata.h                 |  4 ++--
 include/scsi/scsi_host.h               |  6 ++++--
 14 files changed, 29 insertions(+), 55 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 64b3c333aa47..adf5f0697b6b 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -172,19 +172,13 @@ static int hctx_state_show(void *data, struct seq_file *m)
 	return 0;
 }
 
-#define BLK_TAG_ALLOC_NAME(name) [BLK_TAG_ALLOC_##name] = #name
-static const char *const alloc_policy_name[] = {
-	BLK_TAG_ALLOC_NAME(FIFO),
-	BLK_TAG_ALLOC_NAME(RR),
-};
-#undef BLK_TAG_ALLOC_NAME
-
 #define HCTX_FLAG_NAME(name) [ilog2(BLK_MQ_F_##name)] = #name
 static const char *const hctx_flag_name[] = {
 	HCTX_FLAG_NAME(TAG_QUEUE_SHARED),
 	HCTX_FLAG_NAME(STACKING),
 	HCTX_FLAG_NAME(TAG_HCTX_SHARED),
 	HCTX_FLAG_NAME(BLOCKING),
+	HCTX_FLAG_NAME(TAG_RR),
 	HCTX_FLAG_NAME(NO_SCHED_BY_DEFAULT),
 };
 #undef HCTX_FLAG_NAME
@@ -192,22 +186,11 @@ static const char *const hctx_flag_name[] = {
 static int hctx_flags_show(void *data, struct seq_file *m)
 {
 	struct blk_mq_hw_ctx *hctx = data;
-	const int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(hctx->flags);
 
-	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) !=
-			BLK_MQ_F_ALLOC_POLICY_START_BIT);
-	BUILD_BUG_ON(ARRAY_SIZE(alloc_policy_name) != BLK_TAG_ALLOC_MAX);
+	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) != ilog2(BLK_MQ_F_MAX));
 
-	seq_puts(m, "alloc_policy=");
-	if (alloc_policy < ARRAY_SIZE(alloc_policy_name) &&
-	    alloc_policy_name[alloc_policy])
-		seq_puts(m, alloc_policy_name[alloc_policy]);
-	else
-		seq_printf(m, "%d", alloc_policy);
-	seq_puts(m, " ");
-	blk_flags_show(m,
-		       hctx->flags ^ BLK_ALLOC_POLICY_TO_MQ_FLAG(alloc_policy),
-		       hctx_flag_name, ARRAY_SIZE(hctx_flag_name));
+	blk_flags_show(m, hctx->flags, hctx_flag_name,
+			ARRAY_SIZE(hctx_flag_name));
 	seq_puts(m, "\n");
 	return 0;
 }
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index ab4a66791a20..b9f417d980b4 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -545,11 +545,10 @@ static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
 }
 
 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
-				     unsigned int reserved_tags,
-				     int node, int alloc_policy)
+		unsigned int reserved_tags, unsigned int flags, int node)
 {
 	unsigned int depth = total_tags - reserved_tags;
-	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
+	bool round_robin = flags & BLK_MQ_F_TAG_RR;
 	struct blk_mq_tags *tags;
 
 	if (total_tags > BLK_MQ_TAG_MAX) {
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 17f10683d640..2e6132f778fd 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3476,8 +3476,7 @@ static struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
 	if (node == NUMA_NO_NODE)
 		node = set->numa_node;
 
-	tags = blk_mq_init_tags(nr_tags, reserved_tags, node,
-				BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
+	tags = blk_mq_init_tags(nr_tags, reserved_tags, set->flags, node);
 	if (!tags)
 		return NULL;
 
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 3bb9ea80f9b6..c872bbbe6411 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -163,7 +163,7 @@ struct blk_mq_alloc_data {
 };
 
 struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags,
-		unsigned int reserved_tags, int node, int alloc_policy);
+		unsigned int reserved_tags, unsigned int flags, int node);
 void blk_mq_free_tags(struct blk_mq_tags *tags);
 
 unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
index 8f40f75ba08c..06781bdde0d2 100644
--- a/drivers/ata/ahci.h
+++ b/drivers/ata/ahci.h
@@ -396,7 +396,7 @@ extern const struct attribute_group *ahci_sdev_groups[];
 	.shost_groups		= ahci_shost_groups,			\
 	.sdev_groups		= ahci_sdev_groups,			\
 	.change_queue_depth     = ata_scsi_change_queue_depth,		\
-	.tag_alloc_policy       = BLK_TAG_ALLOC_RR,             	\
+	.tag_alloc_policy_rr	= true,					\
 	.device_configure	= ata_scsi_device_configure
 
 extern struct ata_port_operations ahci_ops;
diff --git a/drivers/ata/pata_macio.c b/drivers/ata/pata_macio.c
index f2f36e55a1f4..4b01bb6880b0 100644
--- a/drivers/ata/pata_macio.c
+++ b/drivers/ata/pata_macio.c
@@ -935,7 +935,7 @@ static const struct scsi_host_template pata_macio_sht = {
 	.device_configure	= pata_macio_device_configure,
 	.sdev_groups		= ata_common_sdev_groups,
 	.can_queue		= ATA_DEF_QUEUE,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy_rr	= true,
 };
 
 static struct ata_port_operations pata_macio_ops = {
diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
index b8f363370e1a..21c72650f9cc 100644
--- a/drivers/ata/sata_mv.c
+++ b/drivers/ata/sata_mv.c
@@ -672,7 +672,7 @@ static const struct scsi_host_template mv6_sht = {
 	.dma_boundary		= MV_DMA_BOUNDARY,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth	= ata_scsi_change_queue_depth,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy_rr	= true,
 	.device_configure	= ata_scsi_device_configure
 };
 
diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
index 36d99043ef50..823cce5ea1e9 100644
--- a/drivers/ata/sata_nv.c
+++ b/drivers/ata/sata_nv.c
@@ -385,7 +385,7 @@ static const struct scsi_host_template nv_adma_sht = {
 	.device_configure	= nv_adma_device_configure,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth     = ata_scsi_change_queue_depth,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy_rr	= true,
 };
 
 static const struct scsi_host_template nv_swncq_sht = {
@@ -396,7 +396,7 @@ static const struct scsi_host_template nv_swncq_sht = {
 	.device_configure	= nv_swncq_device_configure,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth     = ata_scsi_change_queue_depth,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy_rr	= true,
 };
 
 /*
diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
index 72c03cbdaff4..935b13e79dec 100644
--- a/drivers/ata/sata_sil24.c
+++ b/drivers/ata/sata_sil24.c
@@ -378,7 +378,6 @@ static const struct scsi_host_template sil24_sht = {
 	.can_queue		= SIL24_MAX_CMDS,
 	.sg_tablesize		= SIL24_MAX_SGE,
 	.dma_boundary		= ATA_DMA_BOUNDARY,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,
 	.sdev_groups		= ata_ncq_sdev_groups,
 	.change_queue_depth	= ata_scsi_change_queue_depth,
 	.device_configure	= ata_scsi_device_configure
diff --git a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
index 79129c977704..35501d0aa655 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
@@ -3345,7 +3345,7 @@ static const struct scsi_host_template sht_v3_hw = {
 	.slave_alloc		= hisi_sas_slave_alloc,
 	.shost_groups		= host_v3_hw_groups,
 	.sdev_groups		= sdev_groups_v3_hw,
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,
+	.tag_alloc_policy_rr	= true,
 	.host_reset             = hisi_sas_host_reset,
 	.host_tagset		= 1,
 	.mq_poll		= queue_complete_v3_hw,
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 5cf124e13097..51c496ca9380 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2065,8 +2065,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 	tag_set->queue_depth = shost->can_queue;
 	tag_set->cmd_size = cmd_size;
 	tag_set->numa_node = dev_to_node(shost->dma_dev);
-	tag_set->flags |=
-		BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
+	if (shost->hostt->tag_alloc_policy_rr)
+		tag_set->flags |= BLK_MQ_F_TAG_RR;
 	if (shost->queuecommand_may_block)
 		tag_set->flags |= BLK_MQ_F_BLOCKING;
 	tag_set->driver_data = shost;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f2ff0ffa0535..a0a9007cc1e3 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -296,13 +296,6 @@ enum blk_eh_timer_return {
 	BLK_EH_RESET_TIMER,
 };
 
-/* Keep alloc_policy_name[] in sync with the definitions below */
-enum {
-	BLK_TAG_ALLOC_FIFO,	/* allocate starting from 0 */
-	BLK_TAG_ALLOC_RR,	/* allocate starting from last allocated tag */
-	BLK_TAG_ALLOC_MAX
-};
-
 /**
  * struct blk_mq_hw_ctx - State for a hardware queue facing the hardware
  * block device
@@ -677,20 +670,19 @@ enum {
 	BLK_MQ_F_TAG_HCTX_SHARED = 1 << 3,
 	BLK_MQ_F_BLOCKING	= 1 << 4,
 
+	/*
+	 * Alloc tags on a round-robin base instead of the first available one.
+	 */
+	BLK_MQ_F_TAG_RR		= 1 << 5,
+
 	/*
 	 * Select 'none' during queue registration in case of a single hwq
 	 * or shared hwqs instead of 'mq-deadline'.
 	 */
 	BLK_MQ_F_NO_SCHED_BY_DEFAULT	= 1 << 6,
-	BLK_MQ_F_ALLOC_POLICY_START_BIT = 7,
-	BLK_MQ_F_ALLOC_POLICY_BITS = 1,
+
+	BLK_MQ_F_MAX = 1 << 7,
 };
-#define BLK_MQ_FLAG_TO_ALLOC_POLICY(flags) \
-	((flags >> BLK_MQ_F_ALLOC_POLICY_START_BIT) & \
-		((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1))
-#define BLK_ALLOC_POLICY_TO_MQ_FLAG(policy) \
-	((policy & ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1)) \
-		<< BLK_MQ_F_ALLOC_POLICY_START_BIT)
 
 #define BLK_MQ_MAX_DEPTH	(10240)
 #define BLK_MQ_NO_HCTX_IDX	(-1U)
diff --git a/include/linux/libata.h b/include/linux/libata.h
index c1a85d46eba6..be5183d75736 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -1467,13 +1467,13 @@ extern const struct attribute_group *ata_common_sdev_groups[];
 #define ATA_SUBBASE_SHT(drv_name)				\
 	__ATA_BASE_SHT(drv_name),				\
 	.can_queue		= ATA_DEF_QUEUE,		\
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,		\
+	.tag_alloc_policy_rr	= true,				\
 	.device_configure	= ata_scsi_device_configure
 
 #define ATA_SUBBASE_SHT_QD(drv_name, drv_qd)			\
 	__ATA_BASE_SHT(drv_name),				\
 	.can_queue		= drv_qd,			\
-	.tag_alloc_policy	= BLK_TAG_ALLOC_RR,		\
+	.tag_alloc_policy_rr	= true,				\
 	.device_configure	= ata_scsi_device_configure
 
 #define ATA_BASE_SHT(drv_name)					\
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 2b4ab0369ffb..02823d6af37d 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -438,8 +438,10 @@ struct scsi_host_template {
 	 */
 	short cmd_per_lun;
 
-	/* If use block layer to manage tags, this is tag allocation policy */
-	int tag_alloc_policy;
+	/*
+	 * Allocate tags starting from last allocated tag.
+	 */
+	bool tag_alloc_policy_rr : 1;
 
 	/*
 	 * Track QUEUE_FULL events and reduce queue depth on demand.
-- 
2.45.2

Re: [PATCH 4/4] block: simplify tag allocation policy selection

[John Garry]

On 06/01/2025 08:35, Christoph Hellwig wrote:
> Use a plain BLK_MQ_F_* flag to select the round robin tag selection
> instead of overlaying an enum with just two possible values into the
> flags space.
> 
> Doing so allows adding a BLK_MQ_F_MAX sentinel for simplified overflow
> checking in the messy debugfs helpers.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

Looks fine, but some small comments still. However, feel free to add:

Reviewed-by: John Garry <john.g.garry@oracle.com>

>   /*
> diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
> index 72c03cbdaff4..935b13e79dec 100644
> --- a/drivers/ata/sata_sil24.c
> +++ b/drivers/ata/sata_sil24.c
> @@ -378,7 +378,6 @@ static const struct scsi_host_template sil24_sht = {
>   	.can_queue		= SIL24_MAX_CMDS,
>   	.sg_tablesize		= SIL24_MAX_SGE,
>   	.dma_boundary		= ATA_DMA_BOUNDARY,
> -	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,

nit: maybe that could be a separate patch, but no biggie

>   	.sdev_groups		= ata_ncq_sdev_groups,
>   	.change_queue_depth	= ata_scsi_change_queue_depth,
>   	.device_configure	= ata_scsi_device_configure
> diff --git a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
> index 79129c977704..35501d0aa655 100644

> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -438,8 +438,10 @@ struct scsi_host_template {
>   	 */
>   	short cmd_per_lun;
>   
> -	/* If use block layer to manage tags, this is tag allocation policy */
> -	int tag_alloc_policy;
> +	/*
> +	 * Allocate tags starting from last allocated tag.
> +	 */
> +	bool tag_alloc_policy_rr : 1;

Is it proper to use bool here? I am not sure. Others use unsigned int or 
unsigned.

nit: coding style elsewhere in scsi_host_template would be to use 
"tag_alloc_policy_rr:1;"

>   
>   	/*
>   	 * Track QUEUE_FULL events and reduce queue depth on demand.

Re: [PATCH 4/4] block: simplify tag allocation policy selection

[Christoph Hellwig]

On Mon, Jan 06, 2025 at 08:50:20AM +0000, John Garry wrote:
>>   	.can_queue		= SIL24_MAX_CMDS,
>>   	.sg_tablesize		= SIL24_MAX_SGE,
>>   	.dma_boundary		= ATA_DMA_BOUNDARY,
>> -	.tag_alloc_policy	= BLK_TAG_ALLOC_FIFO,
>
> nit: maybe that could be a separate patch, but no biggie

I though about that, but if felt a bit overkill.

>> +	/*
>> +	 * Allocate tags starting from last allocated tag.
>> +	 */
>> +	bool tag_alloc_policy_rr : 1;
>
> Is it proper to use bool here? I am not sure. Others use unsigned int or 
> unsigned.

Yes, you can use any unsigned type for a single-bit bitfield.  Most of
the existing uses just predate the availability of bool or were copy
and pasted after that.

>
> nit: coding style elsewhere in scsi_host_template would be to use 
> "tag_alloc_policy_rr:1;"

Yes, but that's against the normal kernel coding style, so we'd better
stop adding more of that.

Re: [PATCH 4/4] block: simplify tag allocation policy selection

[John Garry]

On 06/01/2025 08:55, Christoph Hellwig wrote:
>>> bool tag_alloc_policy_rr : 1;
>> Is it proper to use bool here? I am not sure. Others use unsigned int or
>> unsigned.
> Yes, you can use any unsigned type for a single-bit bitfield.  Most of
> the existing uses just predate the availability of bool or were copy
> and pasted after that.
> 
>> nit: coding style elsewhere in scsi_host_template would be to use
>> "tag_alloc_policy_rr:1;"
> Yes, but that's against the normal kernel coding style, so we'd better
> stop adding more of that.

I suppose then that the rest should be updated afterwards to be 
consistent (with the kernel coding style). That should be easier than - 
for example - removing extern usage.