[PATCH v2 30/45] arm_mpam: resctrl: Pre-allocate assignable monitors

Ben Horgan
2025-12-19T18:14:28Z

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

When there are not enough monitors, MPAM is able to emulate ABMC by making
a smaller number of monitors assignable. These monitors still need to be
allocated from the driver, and mapped to whichever control/monitor group
resctrl wants to use them with.

Add a second array to hold the monitor values indexed by resctrl's cntr_id.

When CDP is in use, two monitors are needed so the available number of
counters halves. Platforms with one monitor will have zero monitors when
CDP is in use.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since rfc:
Move __free
kmalloc -> kcalloc
---
drivers/resctrl/mpam_internal.h | 7 +++
drivers/resctrl/mpam_resctrl.c | 103 ++++++++++++++++++++++++++++++++
2 files changed, 110 insertions(+)

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index c25524f75c2e..a2f6956d9236 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -363,6 +363,13 @@ struct mpam_resctrl_mon {
* un-assigned (closid, rmid) are -1.
*/
int *mbwu_idx_to_mon;
+
+ /*
+ * Array of assigned MBWU monitors, indexed by idx argument.
+ * When ABMC is not in use, this array can be NULL. Otherwise
+ * it maps idx to the allocated monitor.
+ */
+ int *assigned_counters;
};

static inline int mpam_alloc_csu_mon(struct mpam_class *class)
diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
index bea16bc096f7..e96d320c219c 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -50,6 +50,12 @@ static bool exposed_mon_capable;
*/
static bool cdp_enabled;

+/*
+ * L3 local/total may come from different classes - what is the number of MBWU
+ * 'on L3'?
+ */
+static unsigned int l3_num_allocated_mbwu = ~0;
+
/* Whether this num_mbw_mon could result in a free_running system */
static int __mpam_monitors_free_running(u16 num_mbwu_mon)
{
@@ -58,6 +64,15 @@ static int __mpam_monitors_free_running(u16 num_mbwu_mon)
return 0;
}

+/*
+ * If l3_num_allocated_mbwu is forced below PARTID * PMG, then the counters
+ * are not free running, and ABMC's user-interface must be used to assign them.
+ */
+static bool mpam_resctrl_abmc_enabled(void)
+{
+ return l3_num_allocated_mbwu < resctrl_arch_system_num_rmid_idx();
+}
+
bool resctrl_arch_alloc_capable(void)
{
return exposed_alloc_capable;
@@ -102,9 +117,26 @@ static void resctrl_reset_task_closids(void)
read_unlock(&tasklist_lock);
}

+static void mpam_resctrl_monitor_sync_abmc_vals(struct rdt_resource *l3)
+{
+ l3->mon.num_mbm_cntrs = l3_num_allocated_mbwu;
+ if (cdp_enabled)
+ l3->mon.num_mbm_cntrs /= 2;
+
+ if (l3->mon.num_mbm_cntrs) {
+ l3->mon.mbm_cntr_assignable = mpam_resctrl_abmc_enabled();
+ l3->mon.mbm_assign_on_mkdir = mpam_resctrl_abmc_enabled();
+ } else {
+ l3->mon.mbm_cntr_assignable = false;
+ l3->mon.mbm_assign_on_mkdir = false;
+ }
+}
+
int resctrl_arch_set_cdp_enabled(enum resctrl_res_level ignored, bool enable)
{
u32 partid_i = RESCTRL_RESERVED_CLOSID, partid_d = RESCTRL_RESERVED_CLOSID;
+ struct mpam_resctrl_res *res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
+ struct rdt_resource *l3 = &res->resctrl_res;

cdp_enabled = enable;

@@ -120,6 +152,7 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level ignored, bool enable)
WRITE_ONCE(arm64_mpam_global_default, mpam_get_regval(current));

resctrl_reset_task_closids();
+ mpam_resctrl_monitor_sync_abmc_vals(l3);

return 0;
}
@@ -315,6 +348,11 @@ static bool class_has_usable_mbwu(struct mpam_class *class)
return true;
}

+ if (cprops->num_mbwu_mon) {
+ pr_debug("monitors usable via ABMC assignment\n");
+ return true;
+ }
+
return false;
}

@@ -583,6 +621,8 @@ static int __alloc_mbwu_mon(struct mpam_class *class, int *array,
array[i] = mbwu_mon;
}

+ l3_num_allocated_mbwu = min(l3_num_allocated_mbwu, num_mbwu_mon);
+
return 0;
}

@@ -725,6 +765,23 @@ static void mpam_resctrl_pick_counters(void)
mpam_resctrl_counters[QOS_L3_MBM_TOTAL_EVENT_ID].class);
}

+bool resctrl_arch_mbm_cntr_assign_enabled(struct rdt_resource *r)
+{
+ if (r != &mpam_resctrl_controls[RDT_RESOURCE_L3].resctrl_res)
+ return false;
+
+ return mpam_resctrl_abmc_enabled();
+}
+
+int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable)
+{
+ lockdep_assert_cpus_held();
+
+ WARN_ON_ONCE(1);
+
+ return 0;
+}
+
static int mpam_resctrl_control_init(struct mpam_resctrl_res *res,
enum resctrl_res_level type)
{
@@ -804,6 +861,42 @@ static int mpam_resctrl_pick_domain_id(int cpu, struct mpam_component *comp)
return comp->comp_id;
}

+/*
+ * This must run after all event counters have been picked so that any free
+ * running counters have already been allocated.
+ */
+static int mpam_resctrl_monitor_init_abmc(struct mpam_resctrl_mon *mon)
+{
+ struct mpam_resctrl_res *res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
+ struct rdt_resource *l3 = &res->resctrl_res;
+ struct mpam_class *class = mon->class;
+ u16 num_mbwu_mon;
+
+ if (mon->mbwu_idx_to_mon) {
+ pr_debug("monitors free running\n");
+ return 0;
+ }
+
+ int *rmid_array __free(kfree) =
+ kcalloc(resctrl_arch_system_num_rmid_idx(), sizeof(int), GFP_KERNEL);
+
+ if (!rmid_array) {
+ pr_debug("Failed to allocate RMID array\n");
+ return -ENOMEM;
+ }
+ memset(rmid_array, -1, resctrl_arch_system_num_rmid_idx() * sizeof(int));
+
+ num_mbwu_mon = class->props.num_mbwu_mon;
+ mon->assigned_counters = __alloc_mbwu_array(mon->class, num_mbwu_mon);
+ if (IS_ERR(mon->assigned_counters))
+ return PTR_ERR(mon->assigned_counters);
+ mon->mbwu_idx_to_mon = no_free_ptr(rmid_array);
+
+ mpam_resctrl_monitor_sync_abmc_vals(l3);
+
+ return 0;
+}
+
static void mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
enum resctrl_event_id type)
{
@@ -845,6 +938,16 @@ static void mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
* space.
*/
l3->mon.num_rmid = 1;
+
+ switch (type) {
+ case QOS_L3_MBM_LOCAL_EVENT_ID:
+ case QOS_L3_MBM_TOTAL_EVENT_ID:
+ mpam_resctrl_monitor_init_abmc(mon);
+
+ return;
+ default:
+ return;
+ }
}
}

--
2.43.0