[PATCH v4 5/6] nvme: add 'latency' iopolicy

[John Meneghini]

From: Hannes Reinecke <hare@xxxxxxxxxx>

Add a latency-based I/O policy for multipathing. It uses the blk-nodelat
latency tracker to provide latencies for each node, and schedules
I/O on the path with the least latency for the submitting node.

Signed-off-by: Hannes Reinecke <hare@xxxxxxxxxx>
[jmeneghi: fix CONFIG_BLK_NODE_LATENCY n and add latency iopolicy to modinfo]
Signed-off-by: John Meneghini <jmeneghi@xxxxxxxxxx>
---
 drivers/nvme/host/multipath.c | 62 ++++++++++++++++++++++++++++++-----
 drivers/nvme/host/nvme.h      |  1 +
 2 files changed, 55 insertions(+), 8 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 8702a40a1971..e9330bb1990b 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -18,6 +18,7 @@ static const char *nvme_iopolicy_names[] = {
 	[NVME_IOPOLICY_NUMA]	= "numa",
 	[NVME_IOPOLICY_RR]	= "round-robin",
 	[NVME_IOPOLICY_QD]      = "queue-depth",
+	[NVME_IOPOLICY_LAT]	= "latency",
 };
 
 static int iopolicy = NVME_IOPOLICY_NUMA;
@@ -32,6 +33,10 @@ static int nvme_set_iopolicy(const char *val, const struct kernel_param *kp)
 		iopolicy = NVME_IOPOLICY_RR;
 	else if (!strncmp(val, "queue-depth", 11))
 		iopolicy = NVME_IOPOLICY_QD;
+#ifdef CONFIG_BLK_NODE_LATENCY
+	else if (!strncmp(val, "latency", 7))
+		iopolicy = NVME_IOPOLICY_LAT;
+#endif
 	else
 		return -EINVAL;
 
@@ -43,10 +48,36 @@ static int nvme_get_iopolicy(char *buf, const struct kernel_param *kp)
 	return sprintf(buf, "%s\n", nvme_iopolicy_names[iopolicy]);
 }
 
+static int nvme_activate_iopolicy(struct nvme_subsystem *subsys, int iopolicy)
+{
+	struct nvme_ns_head *h;
+	struct nvme_ns *ns;
+	bool enable = iopolicy == NVME_IOPOLICY_LAT;
+	int ret = 0;
+
+	mutex_lock(&subsys->lock);
+	list_for_each_entry(h, &subsys->nsheads, entry) {
+		list_for_each_entry_rcu(ns, &h->list, siblings) {
+			if (enable) {
+				ret = blk_nlat_enable(ns->disk);
+				if (ret)
+					break;
+			} else
+				blk_nlat_disable(ns->disk);
+		}
+	}
+	mutex_unlock(&subsys->lock);
+	return ret;
+}
+
 module_param_call(iopolicy, nvme_set_iopolicy, nvme_get_iopolicy,
 	&iopolicy, 0644);
 MODULE_PARM_DESC(iopolicy,
+#if defined(CONFIG_BLK_NODE_LATENCY)
+	"Default multipath I/O policy; 'numa' (default) , 'round-robin', 'queue-depth' or 'latency'");
+#else
 	"Default multipath I/O policy; 'numa' (default) , 'round-robin' or 'queue-depth'");
+#endif
 
 void nvme_mpath_default_iopolicy(struct nvme_subsystem *subsys)
 {
@@ -250,13 +281,16 @@ static struct nvme_ns *__nvme_find_path(struct nvme_ns_head *head, int node)
 {
 	int found_distance = INT_MAX, fallback_distance = INT_MAX, distance;
 	struct nvme_ns *found = NULL, *fallback = NULL, *ns;
+	int iopolicy = READ_ONCE(head->subsys->iopolicy);
 
 	list_for_each_entry_rcu(ns, &head->list, siblings) {
 		if (nvme_path_is_disabled(ns))
 			continue;
 
-		if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_NUMA)
+		if (iopolicy == NVME_IOPOLICY_NUMA)
 			distance = node_distance(node, ns->ctrl->numa_node);
+		else if (iopolicy == NVME_IOPOLICY_LAT)
+			distance = blk_nlat_latency(ns->disk, node);
 		else
 			distance = LOCAL_DISTANCE;
 
@@ -380,8 +414,8 @@ static inline bool nvme_path_is_optimized(struct nvme_ns *ns)
 
 inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
 {
-	int iopolicy = READ_ONCE(head->subsys->iopolicy);
 	int node;
+	int iopolicy = READ_ONCE(head->subsys->iopolicy);
 	struct nvme_ns *ns;
 
 	/*
@@ -400,8 +434,8 @@ inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
 
 	if (iopolicy == NVME_IOPOLICY_RR)
 		return nvme_round_robin_path(head, node, ns);
-
-	if (unlikely(!nvme_path_is_optimized(ns)))
+	if (iopolicy == NVME_IOPOLICY_LAT ||
+	    unlikely(!nvme_path_is_optimized(ns)))
 		return __nvme_find_path(head, node);
 	return ns;
 }
@@ -871,15 +905,18 @@ static ssize_t nvme_subsys_iopolicy_store(struct device *dev,
 {
 	struct nvme_subsystem *subsys =
 		container_of(dev, struct nvme_subsystem, dev);
-	int i;
+	int i, ret;
 
 	for (i = 0; i < ARRAY_SIZE(nvme_iopolicy_names); i++) {
 		if (sysfs_streq(buf, nvme_iopolicy_names[i])) {
-			nvme_subsys_iopolicy_update(subsys, i);
-			return count;
+			ret = nvme_activate_iopolicy(subsys, i);
+			if (!ret) {
+				nvme_subsys_iopolicy_update(subsys, i);
+				return count;
+			}
+			return ret;
 		}
 	}
-
 	return -EINVAL;
 }
 SUBSYS_ATTR_RW(iopolicy, S_IRUGO | S_IWUSR,
@@ -915,6 +952,15 @@ static int nvme_lookup_ana_group_desc(struct nvme_ctrl *ctrl,
 
 void nvme_mpath_add_disk(struct nvme_ns *ns, __le32 anagrpid)
 {
+	if (!blk_nlat_init(ns->disk) &&
+	    READ_ONCE(ns->head->subsys->iopolicy) == NVME_IOPOLICY_LAT) {
+		int ret = blk_nlat_enable(ns->disk);
+
+		if (unlikely(ret))
+			pr_warn("%s: Failed to enable latency tracking, error %d\n",
+				ns->disk->disk_name, ret);
+	}
+
 	if (nvme_ctrl_use_ana(ns->ctrl)) {
 		struct nvme_ana_group_desc desc = {
 			.grpid = anagrpid,
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 4e876524726a..56b78f21406a 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -406,6 +406,7 @@ enum nvme_iopolicy {
 	NVME_IOPOLICY_NUMA,
 	NVME_IOPOLICY_RR,
 	NVME_IOPOLICY_QD,
+	NVME_IOPOLICY_LAT,
 };
 
 struct nvme_subsystem {
-- 
2.39.3