Re: [RFC v2] arm,x86,fs/resctrl: Generic schema description Proof of Concept

[Reinette Chatre]

Hi Ben,

On 8/5/26 9:59 AM, Ben Horgan wrote:
> Just given a go at running this on a model with MPAM and I can mount resctrl with this
> small patch to initialise the emulated_by lists so that list_empty() behaves.
> 
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index 21dcbf5764cc..638095649151 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -1018,6 +1018,7 @@ static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
>         case RDT_RESOURCE_L3:
>                 mpam_ctrl->r_ctrl.type = RESCTRL_CTRL_BITMAP;
>                 mpam_ctrl->r_ctrl.name = RESCTRL_CTRL_NAME_DEF;
> +               INIT_LIST_HEAD(&mpam_ctrl->r_ctrl.emulated_by);
>                 INIT_LIST_HEAD_RCU(&mpam_ctrl->r_ctrl.domains);
>                 __set_bit(RESCTRL_BITMAP_FLAG_SPARSE, mpam_ctrl->r_ctrl.bitmap.flags);
>                 mpam_ctrl->r_ctrl.bitmap.cbm_len = class->props.cpbm_wd;
> @@ -1048,6 +1049,7 @@ static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
>                 r->ctrl_scope = RESCTRL_L3_CACHE;
>                 mpam_ctrl->r_ctrl.type = RESCTRL_CTRL_SCALAR;
>                 mpam_ctrl->r_ctrl.name = RESCTRL_CTRL_NAME_DEF;
> +               INIT_LIST_HEAD(&mpam_ctrl->r_ctrl.emulated_by);
>                 INIT_LIST_HEAD_RCU(&mpam_ctrl->r_ctrl.domains);
> 
>                 r->bw_throttle_mode = THREAD_THROTTLE_UNDEFINED;

Thank you for this. Added this and it is now available in branch resctrl/controls_rfc_v2.1

> I haven't a good look at the code yet but from the list of changes you have above it seems to be
> heading in the right direction. Thank you for all the work on this and for always considering MPAM
> in the design. I'm out of office for a couple of weeks but I'll give this a better look when I'm back.
> 
> One little thing that seems odd is that control_mode shows 'native' as an option even if there are
> no emulated controls.
> $ cat info/L3/control_mode
> [legacy] native
> 
Yes, that is odd. Especially for the L3 resource that, on top of not having no emulated controls, does not
even support switching of the control mode. I'll fix this. Thank you very much.

Reinette