arm_mpam: resctrl: Pick classes for use as MBM counters

resctrl has two types of bandwidth counters, NUMA-local and global. MPAM
can only count globally; either using MSC at the L3 cache or in the memory
controllers. When global and local equate to the same thing continue just
to call it global.

Pick the corresponding MPAM classes to back the MBM counters. As resctrl
requires all monitors to be at the L3 cache, we can only use the counters
at the memory controllers when they have the same topology as the L3 cache
and the traffic they see if the same. In particular, for the bandwidth
counters at the memory controllers to be exposed to resctrl it is required
there is a single L3 cache and a single NUMA node as otherwise cross NUMA
traffic will be counted at the wrong instance.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Zeng Heng <zengheng4@huawei.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>

drivers/resctrl/mpam_resctrl.c

@@ -606,6 +606,16 @@ static bool cache_has_usable_csu(struct mpam_class *class)
 	return true;
 }
 
+static bool class_has_usable_mbwu(struct mpam_class *class)
+{
+	struct mpam_props *cprops = &class->props;
+
+	if (!mpam_has_feature(mpam_feat_msmon_mbwu, cprops))
+		return false;
+
+	return true;
+}
+
 /*
  * Calculate the worst-case percentage change from each implemented step
  * in the control.
@@ -983,6 +993,24 @@ static void mpam_resctrl_pick_counters(void)
 				break;
 			}
 		}
+
+		if (class_has_usable_mbwu(class) &&
+		    topology_matches_l3(class) &&
+		    traffic_matches_l3(class)) {
+			pr_debug("class %u has usable MBWU, and matches L3 topology and traffic\n",
+				 class->level);
+
+			/*
+			 * An MSC measures bandwidth for a path determined by
+			 * its location in hardware. We can't distinguish
+			 * traffic by destination so we don't know if it's
+			 * staying on the same NUMA node. Hence, we can't
+			 * calculate mbm_local except when we only have one L3
+			 * and it's equivalent to mbm_total and so always use
+			 * mbm_total.
+			 */
+			counter_update_class(QOS_L3_MBM_TOTAL_EVENT_ID, class);
+		}
 	}
 }