Re: [RFC PATCH v2 1/5] arm_mpam: resctrl: Pick classes for use as mbm counters

[Shaopeng Tan (Fujitsu)]

Hello Ben,


> 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@xxxxxxxxxxxxxx>
> Tested-by: Zeng Heng <zengheng4@xxxxxxxxxx>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
> ---
> 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 a7691c66553a..c17577e52f58 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -598,6 +598,16 @@ 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.
> @@ -981,6 +991,22 @@ 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
> 
> 

There are environments with multiple L3 caches within a single NUMA node.
In this case, mbm_total will be the sum of traffic from all caches within that NUAM node.
Is my understanding correct?


Best regards,
Shaopeng TAN