From 436d111d918ae106d7545b1fad6fe42294447603 Mon Sep 17 00:00:00 2001 From: James Morse Date: Fri, 31 Jul 2026 18:52:38 +0100 Subject: [PATCH] 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 Signed-off-by: Ben Horgan Tested-by: Shaopeng Tan Tested-by: Zeng Heng Tested-by: Fenghua Yu Tested-by: Gavin Shan Reviewed-by: Shaopeng Tan Reviewed-by: Jonathan Cameron Reviewed-by: Fenghua Yu Reviewed-by: Gavin Shan Signed-off-by: Will Deacon --- 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); + } } }