Re: [PATCH v3 31/47] arm_mpam: resctrl: Pre-allocate assignable monitors

Shaopeng Tan (Fujitsu)
2026-01-16T10:34:29Z

Hello Ben,

> 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.
>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> 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
>
> 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 | 97 +++++++++++++++++++++++++++++++++
> 2 files changed, 104 insertions(+)
>
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 89f9d374ded0..58076abd5de3 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -367,6 +367,13 @@ 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 3af12ad77fba..2a9efc6c6fae 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -68,6 +68,12 @@ static bool cdp_enabled;
> static bool cacheinfo_ready;
> static DECLARE_WAIT_QUEUE_HEAD(wait_cacheinfo_ready);
>
> +/*
> + * 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)
> {
> @@ -76,6 +82,15 @@ 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;
> @@ -120,9 +135,26 @@ 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;
>
> @@ -138,6 +170,7 @@ 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;
> }
> @@ -321,6 +354,11 @@ 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;
> }
>
> @@ -597,6 +635,8 @@ 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;
> }
>
> @@ -736,6 +776,19 @@ 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)
> +{
> + return -EINVAL;
> +}

$ echo "default" | sudo tee /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
default
tee: /sys/fs/resctrl/info/L3_MON/mbm_assign_mode:Invalid argument
"return -EOPNOTSUPP;" might be better.

Best regards,
Shaopeng TAN

> static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
> {
> struct mpam_class *class = res->class;
> @@ -811,6 +864,42 @@ 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) =
> + 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)
> {
> @@ -857,6 +946,14 @@ static int mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
> * group can be allocated freely:
> */
> l3->mon.num_rmid = mpam_pmg_max + 1;
> +
> + switch (type) {
> + case QOS_L3_MBM_LOCAL_EVENT_ID:
> + case QOS_L3_MBM_TOTAL_EVENT_ID:
> + return mpam_resctrl_monitor_init_abmc(mon);
> + default:
> + return 0;
> + }
> }
>
> return 0;
> --
> 2.43.0