[PATCH v3 1/5] arm_mpam: resctrl: Pick classes for use as mbm counters

[Shaopeng Tan (Fujitsu)]

Hello Ben,

> From: James Morse <james.morse at arm.com>
> 
> resctrl has two types of counters, NUMA-local and global. MPAM can only
> count global either using MSC at the L3 cache or in the memory controllers.
> When global and local equate to the same thing continue just to call it
> global.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng at jp.fujitsu.com>
> Tested-by: Zeng Heng <zengheng4 at huawei.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng at jp.fujitsu.com>
> 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 v1:
> Move finding any_mon_comp into monitor boilerplate patch
> Move mpam_resctrl_get_domain_from_cpu() into monitor boilerplate
> Remove free running check
> Trim commit message
> ---
>  drivers/resctrl/mpam_resctrl.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index 226ff6f532fa..f70fa65d39e4 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -606,6 +606,16 @@ static bool cache_has_usable_csu(struct mpam_class *class)
>          return true;
>  }
>  
> +static bool class_has_usable_mbwu(struct mpam_class *class)
> +{
> +       struct mpam_props *cprops = &class->props;
> +
> +       if (!mpam_has_feature(mpam_feat_msmon_mbwu, cprops))
> +               return false;
> +
> +       return true;
> +}
> +
>  /*
>   * Calculate the worst-case percentage change from each implemented step
>   * in the control.
> @@ -983,6 +993,22 @@ static void mpam_resctrl_pick_counters(void)
>                                  break;
>                          }
>                  }
> +
> +               if (class_has_usable_mbwu(class) &&
> +                   topology_matches_l3(class) &&
> +                   traffic_matches_l3(class)) {
> +                       pr_debug("class %u has usable MBWU, and matches L3 topology and traffic\n",
> +                                class->level);
> +
> +                       /*
> +                        * We can't distinguish traffic by destination so
> +                        * we don't know if it's staying on the same NUMA
> +                        * node. Hence, we can't calculate mbm_local except
> +                        * when we only have one L3 and it's equivalent to
> +                        * mbm_total and so always use mbm_total.
> +                        */
> +                       counter_update_class(QOS_L3_MBM_TOTAL_EVENT_ID, class);
> +               }
>          }
>  }
>  
> -- 
> 2.43.0

https://lore.kernel.org/lkml/599617aa-aade-4fde-9efa-79d592f1ff3f@arm.com/

This concerns the comment I received last time. 
I may not have fully understood it, so I'd like to clarify it once more.

Even if the system as a whole has multiple L3 caches and multiple NUMA nodes,
ABMC will be enabled as long as there is a single L3 cache and a single corresponding NUMA node.
Is my understanding correct?
If my understanding is correct, within the 'traffic_matches_l3()' function,
ABMC is enabled only when the entire system has a single NUMA node and a single L3 cache.

 870 static bool traffic_matches_l3(struct mpam_class *class)
 871 {
...
 901
 902         if (!cpumask_equal(tmp_cpumask, cpu_possible_mask)) {
 903                 pr_debug("There is more than one L3\n");
 904                 return false; *
 905         }
...
 912
 913         if (num_possible_nodes() > 1) {
 914                 pr_debug("There is more than one numa node\n");
 915                 return false;  *
 916         }
 917
...
 926 }


Also, I'd also like to confirm one more thing.
The mpam_resctrl_pick_mba() function also calls traffic_matches_l3(). 
This suggests that, except in scenarios where the entire system has a single L3 cache and a single NUMA node (ABMC is disabled),
the Memory Bandwidth allocation will also be disabled.
Is this the intended behavior? If so, could you explain why?

Best regards,
Shaopeng TAN