[RFC PATCH v1 1/4] arm_mpam: resctrl: Pre-allocate assignable monitors
Ben Horgan
ben.horgan at arm.com
Wed Feb 25 12:54:33 PST 2026
From: James Morse <james.morse at 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.
Reviewed-by: Jonathan Cameron <jonathan.cameron at huawei.com>
Signed-off-by: James Morse <james.morse at arm.com>
Signed-off-by: Ben Horgan <ben.horgan at arm.com>
---
Changes since rfc:
Move __free
kmalloc -> kcalloc
Changes since v2:
kcalloc -> kmalloc_array
sizeof(*rmid_array)
Return error from resctrl_arch_mbm_cntr_assign_set()
---
drivers/resctrl/mpam_internal.h | 7 +++
drivers/resctrl/mpam_resctrl.c | 93 +++++++++++++++++++++++++++++++--
2 files changed, 96 insertions(+), 4 deletions(-)
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 195ab821cc52..9c4dc0684f6d 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -417,6 +417,13 @@ struct mpam_resctrl_mon {
/* Array of allocated MBWU monitors, indexed by (closid, rmid). */
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 afe43034a516..58fd3ee10fd2 100644
--- a/drivers/resctrl/mpam_resctrl.c
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -75,6 +75,12 @@ static DECLARE_WAIT_QUEUE_HEAD(wait_cacheinfo_ready);
*/
static bool resctrl_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)
{
@@ -83,6 +89,15 @@ 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)
{
struct mpam_resctrl_res *res;
@@ -143,7 +158,10 @@ int resctrl_arch_cntr_read(struct rdt_resource *r, struct rdt_l3_mon_domain *d,
bool resctrl_arch_mbm_cntr_assign_enabled(struct rdt_resource *r)
{
- return false;
+ 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)
@@ -188,9 +206,26 @@ 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 rid, 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;
int cpu;
/* This resctrl hook is only called with enable set to false on error */
@@ -217,6 +252,7 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable)
WRITE_ONCE(arm64_mpam_global_default, mpam_get_regval(current));
resctrl_reset_task_closids();
+ mpam_resctrl_monitor_sync_abmc_vals(l3);
for_each_possible_cpu(cpu)
mpam_set_cpu_defaults(cpu, partid_d, partid_i, 0, 0);
@@ -667,7 +703,10 @@ static bool class_has_usable_mbwu(struct mpam_class *class)
return true;
}
- pr_debug("Insufficient monitors for free-running mode\n");
+ if (cprops->num_mbwu_mon) {
+ pr_debug("monitors usable via ABMC assignment\n");
+ return true;
+ }
return false;
}
@@ -1010,6 +1049,8 @@ 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;
}
@@ -1214,9 +1255,46 @@ 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) =
+ kmalloc_array(resctrl_arch_system_num_rmid_idx(), sizeof(*rmid_array), 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 int mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
enum resctrl_event_id type)
{
+ int err = 0;
struct mpam_resctrl_res *res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
struct rdt_resource *l3 = &res->resctrl_res;
@@ -1259,8 +1337,15 @@ static int mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
*/
l3->mon.num_rmid = resctrl_arch_system_num_rmid_idx();
- if (resctrl_enable_mon_event(type, false, 0, NULL))
- l3->mon_capable = true;
+ if (type == QOS_L3_MBM_TOTAL_EVENT_ID)
+ err = mpam_resctrl_monitor_init_abmc(mon);
+ if (err)
+ return err;
+
+ if (!resctrl_enable_mon_event(type, false, 0, NULL))
+ return -EINVAL;
+
+ l3->mon_capable = true;
return 0;
}
--
2.43.0
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