[PATCH 2/2] nvme: multipath: round-robin: don't fall back to numa

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

Currently, if the RR path selector returns a non-optimized path,
we fall back to __nvme_find_path(), which uses the logic of the
numa path selector. For a given numa node, this always chooses
the same path, thus preventing round-robin logic on non-optimized
paths.

By handling the situation where the current ns is NULL in
nvme_round_robin_path(), we can avoid falling back from round-robin
to NUMA, fixing the issue. The iopolicy case distinction in
__nvme_find_path() can be skipped now.

Signed-off-by: Martin Wilck <mwilck at suse.com>
---
 drivers/nvme/host/multipath.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 2c575b783d3e..ff93bab0d549 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -181,10 +181,7 @@ static struct nvme_ns *__nvme_find_path(struct nvme_ns_head *head, int node)
 		if (nvme_path_is_disabled(ns))
 			continue;
 
-		if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_NUMA)
-			distance = node_distance(node, ns->ctrl->numa_node);
-		else
-			distance = LOCAL_DISTANCE;
+		distance = node_distance(node, ns->ctrl->numa_node);
 
 		switch (ns->ana_state) {
 		case NVME_ANA_OPTIMIZED:
@@ -225,7 +222,13 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head,
 		int node, struct nvme_ns *old)
 {
 	struct nvme_ns *ns, *found = NULL;
+	bool was_null = (old == NULL);
 
+	if (unlikely(was_null))
+		old = list_first_or_null_rcu(&head->list,
+					     struct nvme_ns, siblings);
+	if (unlikely(!old))
+		return NULL;
 
 	for (ns = nvme_next_ns(head, old);
 	     ns != old;
@@ -244,9 +247,12 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head,
 	/* Fall back to old if it's better than the others */
 	if (!nvme_path_is_disabled(old) &&
 	    (old->ana_state == NVME_ANA_OPTIMIZED ||
-	     (!found && old->ana_state == NVME_ANA_NONOPTIMIZED)))
+	     (!found && old->ana_state == NVME_ANA_NONOPTIMIZED))) {
 		found = old;
-
+		if (!was_null)
+			/* No need to switch */
+			return found;
+	}
 	if (!found)
 		return NULL;
 
@@ -267,8 +273,9 @@ inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
 	struct nvme_ns *ns;
 
 	ns = srcu_dereference(head->current_path[node], &head->srcu);
-	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR && ns)
-		ns = nvme_round_robin_path(head, node, ns);
+	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR)
+		return nvme_round_robin_path(head, node, ns);
+
 	if (unlikely(!ns || !nvme_path_is_optimized(ns)))
 		ns = __nvme_find_path(head, node);
 	return ns;
-- 
2.26.2