Hi Jonathan,

On 1/6/26 14:29, Jonathan Cameron wrote:

On Fri, 19 Dec 2025 18:11:32 +0000
Ben Horgan [off-list ref] wrote:

quoted

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
 

Trivial comments only,
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>

quoted

 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

quoted

+/*
+ * 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);

It's a long line, but I'd prefer sizeof(*rmid_array).
could use kmalloc_array to avoid zeroing just before you fill it with -1.

Nice, I hadn't found kmalloc_array().

quoted

+
+	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;
+}

Thanks,

Ben