[PATCH] acpi/hmat,mm/memtier: always register hmat adist calculation callback

[Gregory Price <gourry@gourry.net>]

In the event that hmat data is not available for the DRAM tier,
or if it is invalid (bandwidth or latency is 0), we can still register
a callback to calculate the abstract distance for non-cpu nodes
and simply assign it a different tier manually.

In the case where DRAM HMAT values are missing or not sane we
manually assign adist=(MEMTIER_ADISTANCE_DRAM + MEMTIER_CHUNK_SIZE).

If the HMAT data for the non-cpu tier is invalid (e.g. bw = 0), we
cannot reasonable determine where to place the tier, so it will default
to MEMTIER_ADISTANCE_DRAM (which is the existing behavior).

Signed-off-by: Gregory Price <gourry@gourry.net>
---
 drivers/acpi/numa/hmat.c |  6 ++++--
 mm/memory-tiers.c        | 10 ++++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
index 2c8ccc91ebe6..1642d2bd83b5 100644
--- a/drivers/acpi/numa/hmat.c
+++ b/drivers/acpi/numa/hmat.c
@@ -1080,8 +1080,10 @@ static __init int hmat_init(void)
 	if (hotplug_memory_notifier(hmat_callback, HMAT_CALLBACK_PRI))
 		goto out_put;
 
-	if (!hmat_set_default_dram_perf())
-		register_mt_adistance_algorithm(&hmat_adist_nb);
+	if (hmat_set_default_dram_perf())
+		pr_notice("Failed to set default dram perf\n");
+
+	register_mt_adistance_algorithm(&hmat_adist_nb);
 
 	return 0;
 out_put:
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 6632102bd5c9..43bd508938ae 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -765,8 +765,14 @@ int mt_perf_to_adistance(struct access_coordinate *perf, int *adist)
 	    perf->read_bandwidth + perf->write_bandwidth == 0)
 		return -EINVAL;
 
-	if (default_dram_perf_ref_nid == NUMA_NO_NODE)
-		return -ENOENT;
+	/*
+	 * If the DRAM tier did not have valid HMAT data, we can instead just
+	 * assume that the non-cpu numa nodes are 1 tier below cpu nodes
+	 */
+	if (default_dram_perf_ref_nid == NUMA_NO_NODE) {
+		*adist = MEMTIER_ADISTANCE_DRAM + MEMTIER_CHUNK_SIZE;
+		return 0;
+	}
 
 	/*
 	 * The abstract distance of a memory node is in direct proportion to
-- 
2.43.0