[RFC PATCH v2 2/5] arm_mpam: resctrl: Pre-allocate assignable monitors
Shaopeng Tan (Fujitsu)
tan.shaopeng at fujitsu.com
Thu Mar 26 20:00:41 PDT 2026
Hello Ben,
> MPAM is able to emulate ABMC, i.e. mbm_event mode, by making memory
> bandwidth monitors assignable. Rather than supporting the 'default'
> mbm_assign_mode always use 'mbm_event'mode even if there are sufficient
> memory bandwidth monitors. The per monitor event configuration is only
> provided by resctrl when in 'mbm_event' mode and so only allowing
> 'mbm_event' mode will make it easier to support per-monitor event
> configuration for MPAM. For the moment, the only event supported is
> mbm_total_event with no bandwidth type configuration. The 'mbm_assign_mode'
> file will still show 'default' when there is no support for memory
> bandwidth monitoring.
>
> The monitors 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.
>
> Co-developed-by: James Morse <james.morse at arm.com>
> Signed-off-by: James Morse <james.morse at arm.com>
> Signed-off-by: Ben Horgan <ben.horgan at arm.com>
> ---
> Changes since rfc v1:
> abmc enabled even if enough counters
> Helpers from dropped free running commits
> carry on with zero counters if using cdp
> set config bits
> use kmalloc_objs
> drop tags for rework
> Configure mbm_cntr_configurable, mbm_cntr_assign_fixed
> ---
> drivers/resctrl/mpam_internal.h | 6 +-
> drivers/resctrl/mpam_resctrl.c | 135 +++++++++++++++++++++++++++++++-
> 2 files changed, 137 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index dbb99d9b0795..02807531bd1b 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -415,7 +415,11 @@ struct mpam_resctrl_res {
> struct mpam_resctrl_mon {
> struct mpam_class *class;
>
> - /* per-class data that resctrl needs will live here */
> + /* Array of allocated MBWU monitors, indexed by (closid, rmid). */
> + int *mbwu_idx_to_mon;
> +
> + /* Array of assigned MBWU monitors, indexed by idx argument. */
> + 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 c17577e52f58..74b6ca59ce4a 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -75,6 +75,8 @@ static DECLARE_WAIT_QUEUE_HEAD(wait_cacheinfo_ready);
> */
> static bool resctrl_enabled;
>
> +static unsigned int l3_num_allocated_mbwu = ~0;
> +
> bool resctrl_arch_alloc_capable(void)
> {
> struct mpam_resctrl_res *res;
> @@ -140,7 +142,7 @@ 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;
> + return (r == &mpam_resctrl_controls[RDT_RESOURCE_L3].resctrl_res);
> }
>
> int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable)
> @@ -185,6 +187,22 @@ 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;
> +
> + /*
> + * Continue as normal even if there are zero counters to avoid giving
> + * resctrl mixed messages.
> + */
> + l3->mon.mbm_cntr_assignable = true;
> + l3->mon.mbm_assign_on_mkdir = true;
> + l3->mon.mbm_cntr_configurable = false;
> + l3->mon.mbm_cntr_assign_fixed = true;
> +}
> +
> int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable)
> {
> u32 partid_i = RESCTRL_RESERVED_CLOSID, partid_d = RESCTRL_RESERVED_CLOSID;
> @@ -236,6 +254,7 @@ 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);
Why is ABMC supported by default when CDP is enabled?
> for_each_possible_cpu(cpu)
> mpam_set_cpu_defaults(cpu, partid_d, partid_i, 0, 0);
> @@ -605,6 +624,9 @@ static bool class_has_usable_mbwu(struct mpam_class *class)
> if (!mpam_has_feature(mpam_feat_msmon_mbwu, cprops))
> return false;
>
> + if (!cprops->num_mbwu_mon)
> + return false;
> +
> return true;
> }
>
> @@ -933,6 +955,52 @@ static void mpam_resctrl_pick_mba(void)
> }
> }
>
> +static void __free_mbwu_mon(struct mpam_class *class, int *array,
> + u16 num_mbwu_mon)
> +{
> + for (int i = 0; i < num_mbwu_mon; i++) {
> + if (array[i] < 0)
> + continue;
> +
> + mpam_free_mbwu_mon(class, array[i]);
> + array[i] = ~0;
> + }
> +}
> +
> +static int __alloc_mbwu_mon(struct mpam_class *class, int *array,
> + u16 num_mbwu_mon)
> +{
> + for (int i = 0; i < num_mbwu_mon; i++) {
> + int mbwu_mon = mpam_alloc_mbwu_mon(class);
> +
> + if (mbwu_mon < 0) {
> + __free_mbwu_mon(class, array, num_mbwu_mon);
> + return mbwu_mon;
> + }
> + array[i] = mbwu_mon;
> + }
> +
> + l3_num_allocated_mbwu = min(l3_num_allocated_mbwu, num_mbwu_mon);
> +
> + return 0;
> +}
> +
> +static int *__alloc_mbwu_array(struct mpam_class *class, u16 num_mbwu_mon)
> +{
> + int err;
> + int *array __free(kfree) = kmalloc_objs(*array, num_mbwu_mon);
> +
> + if (!array)
> + return ERR_PTR(-ENOMEM);
> +
> + memset(array, -1, num_mbwu_mon * sizeof(*array));
> +
> + err = __alloc_mbwu_mon(class, array, num_mbwu_mon);
> + if (err)
> + return ERR_PTR(err);
> + return_ptr(array);
> +}
> +
> static void counter_update_class(enum resctrl_event_id evt_id,
> struct mpam_class *class)
> {
> @@ -1087,9 +1155,46 @@ 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;
> + size_t num_rmid = resctrl_arch_system_num_rmid_idx();
> +
> + if (mon->mbwu_idx_to_mon) {
> + pr_debug("monitors free running\n");
> + return 0;
> + }
ABMC is not supported under this condition.
Why does this condition conclude that there are enough monitors(monitors freee running)?
Best regards,
Shaopeng TAN
> + int *rmid_array __free(kfree) = kmalloc_objs(*rmid_array, num_rmid);
> +
> + if (!rmid_array) {
> + pr_debug("Failed to allocate RMID array\n");
> + return -ENOMEM;
> + }
> + memset(rmid_array, -1, num_rmid * sizeof(*rmid_array));
> +
> + 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;
>
> @@ -1131,8 +1236,19 @@ 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;
> +
> + static_assert(MAX_EVT_CONFIG_BITS == 0x7f);
> + l3->mon.mbm_cfg_mask = MAX_EVT_CONFIG_BITS;
> + }
> +
> + if (!resctrl_enable_mon_event(type, false, 0, NULL))
> + return -EINVAL;
> +
> + l3->mon_capable = true;
>
> return 0;
> }
> @@ -1695,6 +1811,17 @@ void mpam_resctrl_exit(void)
> resctrl_exit();
> }
>
> +static void mpam_resctrl_teardown_mon(struct mpam_resctrl_mon *mon, struct mpam_class *class)
> +{
> + u32 num_mbwu_mon = resctrl_arch_system_num_rmid_idx();
> +
> + if (!mon->mbwu_idx_to_mon)
> + return;
> +
> + __free_mbwu_mon(class, mon->mbwu_idx_to_mon, num_mbwu_mon);
> + mon->mbwu_idx_to_mon = NULL;
> +}
> +
> /*
> * The driver is detaching an MSC from this class, if resctrl was using it,
> * pull on resctrl_exit().
> @@ -1717,6 +1844,8 @@ void mpam_resctrl_teardown_class(struct mpam_class *class)
> for_each_mpam_resctrl_mon(mon, eventid) {
> if (mon->class == class) {
> mon->class = NULL;
> +
> + mpam_resctrl_teardown_mon(mon, class);
> break;
> }
> }
> --
> 2.43.0
More information about the linux-arm-kernel
mailing list