[PATCH v5 1/5] arm_mpam: resctrl: Pick classes for use as MBM counters

[Ben Horgan]

From: James Morse <james.morse at arm.com>

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 at arm.com>
Signed-off-by: Ben Horgan <ben.horgan at arm.com>
Tested-by: Shaopeng Tan <tan.shaopeng at jp.fujitsu.com>
Tested-by: Zeng Heng <zengheng4 at huawei.com>
Tested-by: Fenghua Yu <fenghuay at nvidia.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng at jp.fujitsu.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron at huawei.com>
Reviewed-by: Fenghua Yu <fenghuay at nvidia.com>
---
Changes since rfc v1:
Move finding any_mon_comp into monitor boilerplate patch
Move mpam_resctrl_get_domain_from_cpu() into monitor boilerplate
Remove free running check
Trim commit message

Changes since v3:
Extra paragraph in commit message

Changes since v4:
Commit message tag ordering
New sentence in block comment (Fenghua)
---
 drivers/resctrl/mpam_resctrl.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index 226ff6f532fa..0fce9703b869 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/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);
+		}
 	}
 }
 
-- 
2.43.0