[PATCH v2 4/7] nvme-multipath: round-robin support for marginal paths

[Jesse Taube <jtaubepe@redhat.com>]

Exclude marginal paths from round-robin io policy. In the case where all
paths are marginal and no optimized or non-optimized path is found, we
fall back and perform round-robin on the marginal paths.

Signed-off-by: Jesse Taube <jtaubepe@redhat.com>
---
V10 -> V1:
 - New commit
V1 -> V2:
 - Rewrite
---
 drivers/nvme/host/multipath.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index f28797deab68..738e3c742b74 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -392,22 +392,29 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head)
 	int node = numa_node_id();
 	struct nvme_ns *old = srcu_dereference(head->current_path[node],
 					       &head->srcu);
+	bool need_marginal;
 
 	if (unlikely(!old))
 		return __nvme_find_path(head, node);
 
 	if (list_is_singular(&head->list)) {
-		if (nvme_path_is_disabled(old))
-			return NULL;
-		return old;
+		if (nvme_path_is_usable(old))
+			return old;
+		return NULL;
 	}
 
+	need_marginal = nvme_all_paths_marginal(head);
+
 	for (ns = nvme_next_ns(head, old);
 	     ns && ns != old;
 	     ns = nvme_next_ns(head, ns)) {
 		if (nvme_path_is_disabled(ns))
 			continue;
 
+		/* Skip marginal paths unless we need to use them */
+		if (!need_marginal && nvme_ctrl_is_marginal(ns->ctrl))
+			continue;
+
 		if (ns->ana_state == NVME_ANA_OPTIMIZED) {
 			found = ns;
 			goto out;
@@ -419,12 +426,23 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head)
 	/*
 	 * The loop above skips the current path for round-robin semantics.
 	 * Fall back to the current path if either:
-	 *  - no other optimized path found and current is optimized,
+	 *  - no other optimized path found and current is,
+	 *      optimized and not marginal.
+	 *  - no other non-marginal path found and current is,
+	 *      optimized and marginal.
 	 *  - no other usable path found and current is usable.
 	 */
-	if (!nvme_path_is_disabled(old) &&
-	    (old->ana_state == NVME_ANA_OPTIMIZED ||
-	     (!found && old->ana_state == NVME_ANA_NONOPTIMIZED)))
+	/* no other usable path found and current is usable. */
+	if (nvme_path_is_usable(old) && !found)
+		return old;
+	/*
+	 *  - no other optimized path found and current is,
+	 *      optimized and not marginal.
+	 *  - no other non-marginal path found and current is,
+	 *      optimized and marginal.
+	 */
+	if (nvme_path_is_usable(old) && old->ana_state == NVME_ANA_OPTIMIZED &&
+	   (!nvme_ctrl_is_marginal(old->ctrl) || need_marginal))
 		return old;
 
 	if (!found)
-- 
2.55.0