block: simplify tag allocation policy selection

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>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20250106083531.799976-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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) !=
+	BUILD_BUG_ON(ARRAY_SIZE(hctx_flag_name) != ilog2(BLK_MQ_F_MAX));
-			BLK_MQ_F_ALLOC_POLICY_START_BIT);
-	BUILD_BUG_ON(ARRAY_SIZE(alloc_policy_name) != BLK_TAG_ALLOC_MAX);
 
-	seq_puts(m, "alloc_policy=");
+	blk_flags_show(m, hctx->flags, hctx_flag_name,
-	if (alloc_policy < ARRAY_SIZE(alloc_policy_name) &&
+			ARRAY_SIZE(hctx_flag_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));
 	seq_puts(m, "\n");
 	return 0;
 }

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,
+		unsigned int reserved_tags, unsigned int flags, int node)
-				     int node, int alloc_policy)
 {
 	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) {

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,
+	tags = blk_mq_init_tags(nr_tags, reserved_tags, set->flags, node);
-				BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
 	if (!tags)
 		return NULL;
 

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);

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;

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 = {

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
 };
 

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,
 };
 
 /*

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

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,

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 |=
+	if (shost->hostt->tag_alloc_policy_rr)
-		BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
+		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;

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)

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)					\

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.