scsi: target: Move LUN stats to per-CPU

The atomic use in the main I/O path is causing perf issues when using
higher performance backend devices and multiple queues (more than
10 when using vhost-scsi) like with this fio workload:

[global]
bs=4K
iodepth=128
direct=1
ioengine=libaio
group_reporting
time_based
runtime=120
name=standard-iops
rw=randread
numjobs=16
cpus_allowed=0-15

To fix this issue, move the LUN stats to per CPU.

Note: I forgot to include this patch with the delayed/ordered per CPU
tracking and per device/device entry per CPU stats. With this patch you
get the full 33% improvements when using fast backends, multiple queues
and multiple IO submiters.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Link: https://patch.msgid.link/20250917221338.14813-4-michael.christie@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_device.c

@@ -814,6 +814,7 @@ struct se_device *target_alloc_device(struct se_hba *hba, const char *name)
 	dev->dev_attrib.max_write_same_len = DA_MAX_WRITE_SAME_LEN;
 	dev->dev_attrib.submit_type = TARGET_FABRIC_DEFAULT_SUBMIT;
 
+	/* Skip allocating lun_stats since we can't export them. */
 	xcopy_lun = &dev->xcopy_lun;
 	rcu_assign_pointer(xcopy_lun->lun_se_dev, dev);
 	init_completion(&xcopy_lun->lun_shutdown_comp);

drivers/target/target_core_fabric_configfs.c

@@ -697,7 +697,7 @@ static void target_fabric_port_release(struct config_item *item)
 	struct se_lun *lun = container_of(to_config_group(item),
 					  struct se_lun, lun_group);
 
-	kfree_rcu(lun, rcu_head);
+	call_rcu(&lun->rcu_head, target_tpg_free_lun);
 }
 
 static struct configfs_item_operations target_fabric_port_item_ops = {

drivers/target/target_core_internal.h

@@ -125,6 +125,7 @@ void	core_tpg_add_node_to_devs(struct se_node_acl *, struct se_portal_group *,
 				  struct se_lun *);
 void	core_tpg_wait_for_nacl_pr_ref(struct se_node_acl *);
 struct se_lun *core_tpg_alloc_lun(struct se_portal_group *, u64);
+void	target_tpg_free_lun(struct rcu_head *head);
 int	core_tpg_add_lun(struct se_portal_group *, struct se_lun *,
 		bool, struct se_device *);
 void core_tpg_remove_lun(struct se_portal_group *, struct se_lun *);

drivers/target/target_core_stat.c

@@ -606,53 +606,30 @@ static ssize_t target_stat_tgt_port_port_index_show(struct config_item *item,
 	return ret;
 }
 
-static ssize_t target_stat_tgt_port_in_cmds_show(struct config_item *item,
+#define tgt_port_show_per_cpu_stat(prefix, field, shift)		\
-		char *page)
+per_cpu_stat_snprintf(scsi_port_stats, prefix, field, shift);		\
-{
+static ssize_t								\
-	struct se_lun *lun = to_stat_tgt_port(item);
+target_stat_##prefix##_show(struct config_item *item, char *page)	\
-	struct se_device *dev;
+{									\
-	ssize_t ret = -ENODEV;
+	struct se_lun *lun = to_stat_tgt_port(item);			\
-
+	struct se_device *dev;						\
-	rcu_read_lock();
+	int ret;							\
-	dev = rcu_dereference(lun->lun_se_dev);
+									\
-	if (dev)
+	rcu_read_lock();						\
-		ret = snprintf(page, PAGE_SIZE, "%lu\n",
+	dev = rcu_dereference(lun->lun_se_dev);				\
-			       atomic_long_read(&lun->lun_stats.cmd_pdus));
+	if (!dev) {							\
-	rcu_read_unlock();
+		rcu_read_unlock();					\
-	return ret;
+		return -ENODEV;						\
+	}								\
+									\
+	ret = per_cpu_stat_##prefix##_snprintf(lun->lun_stats, page);	\
+	rcu_read_unlock();						\
+	return ret;							\
 }
 
-static ssize_t target_stat_tgt_port_write_mbytes_show(struct config_item *item,
+tgt_port_show_per_cpu_stat(tgt_port_in_cmds, cmd_pdus, 0);
-		char *page)
+tgt_port_show_per_cpu_stat(tgt_port_write_mbytes, rx_data_octets, 20);
-{
+tgt_port_show_per_cpu_stat(tgt_port_read_mbytes, tx_data_octets, 20);
-	struct se_lun *lun = to_stat_tgt_port(item);
-	struct se_device *dev;
-	ssize_t ret = -ENODEV;
-
-	rcu_read_lock();
-	dev = rcu_dereference(lun->lun_se_dev);
-	if (dev)
-		ret = snprintf(page, PAGE_SIZE, "%u\n",
-			(u32)(atomic_long_read(&lun->lun_stats.rx_data_octets) >> 20));
-	rcu_read_unlock();
-	return ret;
-}
-
-static ssize_t target_stat_tgt_port_read_mbytes_show(struct config_item *item,
-		char *page)
-{
-	struct se_lun *lun = to_stat_tgt_port(item);
-	struct se_device *dev;
-	ssize_t ret = -ENODEV;
-
-	rcu_read_lock();
-	dev = rcu_dereference(lun->lun_se_dev);
-	if (dev)
-		ret = snprintf(page, PAGE_SIZE, "%u\n",
-				(u32)(atomic_long_read(&lun->lun_stats.tx_data_octets) >> 20));
-	rcu_read_unlock();
-	return ret;
-}
 
 static ssize_t target_stat_tgt_port_hs_in_cmds_show(struct config_item *item,
 		char *page)

drivers/target/target_core_tpg.c

@@ -548,7 +548,7 @@ int core_tpg_register(
 		ret = core_tpg_add_lun(se_tpg, se_tpg->tpg_virt_lun0,
 				true, g_lun0_dev);
 		if (ret < 0) {
-			kfree(se_tpg->tpg_virt_lun0);
+			target_tpg_free_lun(&se_tpg->tpg_virt_lun0->rcu_head);
 			return ret;
 		}
 	}
@@ -595,7 +595,7 @@ int core_tpg_deregister(struct se_portal_group *se_tpg)
 
 	if (se_tpg->proto_id >= 0) {
 		core_tpg_remove_lun(se_tpg, se_tpg->tpg_virt_lun0);
-		kfree_rcu(se_tpg->tpg_virt_lun0, rcu_head);
+		call_rcu(&se_tpg->tpg_virt_lun0->rcu_head, target_tpg_free_lun);
 	}
 
 	target_tpg_deregister_rtpi(se_tpg);
@@ -615,6 +615,13 @@ struct se_lun *core_tpg_alloc_lun(
 		pr_err("Unable to allocate se_lun memory\n");
 		return ERR_PTR(-ENOMEM);
 	}
+
+	lun->lun_stats = alloc_percpu(struct scsi_port_stats);
+	if (!lun->lun_stats) {
+		pr_err("Unable to allocate se_lun stats memory\n");
+		goto free_lun;
+	}
+
 	lun->unpacked_lun = unpacked_lun;
 	atomic_set(&lun->lun_acl_count, 0);
 	init_completion(&lun->lun_shutdown_comp);
@@ -628,6 +635,18 @@ struct se_lun *core_tpg_alloc_lun(
 	lun->lun_tpg = tpg;
 
 	return lun;
+
+free_lun:
+	kfree(lun);
+	return ERR_PTR(-ENOMEM);
+}
+
+void target_tpg_free_lun(struct rcu_head *head)
+{
+	struct se_lun *lun = container_of(head, struct se_lun, rcu_head);
+
+	free_percpu(lun->lun_stats);
+	kfree(lun);
 }
 
 int core_tpg_add_lun(

drivers/target/target_core_transport.c

@@ -1571,7 +1571,12 @@ target_cmd_parse_cdb(struct se_cmd *cmd)
 		return ret;
 
 	cmd->se_cmd_flags |= SCF_SUPPORTED_SAM_OPCODE;
-	atomic_long_inc(&cmd->se_lun->lun_stats.cmd_pdus);
+	/*
+	 * If this is the xcopy_lun then we won't have lun_stats since we
+	 * can't export them.
+	 */
+	if (cmd->se_lun->lun_stats)
+		this_cpu_inc(cmd->se_lun->lun_stats->cmd_pdus);
 	return 0;
 }
 EXPORT_SYMBOL(target_cmd_parse_cdb);
@@ -2597,8 +2602,9 @@ queue_rsp:
 		    !(cmd->se_cmd_flags & SCF_TREAT_READ_AS_NORMAL))
 			goto queue_status;
 
-		atomic_long_add(cmd->data_length,
+		if (cmd->se_lun->lun_stats)
-				&cmd->se_lun->lun_stats.tx_data_octets);
+			this_cpu_add(cmd->se_lun->lun_stats->tx_data_octets,
+				     cmd->data_length);
 		/*
 		 * Perform READ_STRIP of PI using software emulation when
 		 * backend had PI enabled, if the transport will not be
@@ -2621,14 +2627,16 @@ queue_rsp:
 			goto queue_full;
 		break;
 	case DMA_TO_DEVICE:
-		atomic_long_add(cmd->data_length,
+		if (cmd->se_lun->lun_stats)
-				&cmd->se_lun->lun_stats.rx_data_octets);
+			this_cpu_add(cmd->se_lun->lun_stats->rx_data_octets,
+				     cmd->data_length);
 		/*
 		 * Check if we need to send READ payload for BIDI-COMMAND
 		 */
 		if (cmd->se_cmd_flags & SCF_BIDI) {
-			atomic_long_add(cmd->data_length,
+			if (cmd->se_lun->lun_stats)
-					&cmd->se_lun->lun_stats.tx_data_octets);
+				this_cpu_add(cmd->se_lun->lun_stats->tx_data_octets,
+					     cmd->data_length);
 			ret = cmd->se_tfo->queue_data_in(cmd);
 			if (ret)
 				goto queue_full;

include/target/target_core_base.h

@@ -744,9 +744,9 @@ struct se_port_stat_grps {
 };
 
 struct scsi_port_stats {
-	atomic_long_t	cmd_pdus;
+	u64			cmd_pdus;
-	atomic_long_t	tx_data_octets;
+	u64			tx_data_octets;
-	atomic_long_t	rx_data_octets;
+	u64			rx_data_octets;
 };
 
 struct se_lun {
@@ -773,7 +773,7 @@ struct se_lun {
 	spinlock_t		lun_tg_pt_gp_lock;
 
 	struct se_portal_group	*lun_tpg;
-	struct scsi_port_stats	lun_stats;
+	struct scsi_port_stats	__percpu *lun_stats;
 	struct config_group	lun_group;
 	struct se_port_stat_grps port_stat_grps;
 	struct completion	lun_shutdown_comp;