Re: [PATCH v4 15/41] arm_mpam: resctrl: Pick the caches we will use as resctrl resources

Reinette Chatre
2026-02-10T23:39:59Z

Hi Ben,

On 2/3/26 1:43 PM, Ben Horgan wrote:
...
> +
> static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
> {
> - /* TODO: initialise the resctrl resources */
> + struct mpam_class *class = res->class;
> + struct rdt_resource *r = &res->resctrl_res;
> +
> + switch (r->rid) {
> + case RDT_RESOURCE_L2:
> + case RDT_RESOURCE_L3:
> + r->alloc_capable = true;
> + r->schema_fmt = RESCTRL_SCHEMA_BITMAP;
> + r->cache.arch_has_sparse_bitmasks = true;
> +
> + r->cache.cbm_len = class->props.cpbm_wd;
> + /* mpam_devices will reject empty bitmaps */
> + r->cache.min_cbm_bits = 1;
> +
> + if (r->rid == RDT_RESOURCE_L2) {
> + r->name = "L2";

This code is fine but highlights that resctrl fs should not let the
arch need to do this since this name is used as part of user interface.

> + r->ctrl_scope = RESCTRL_L2_CACHE;
> + } else {
> + r->name = "L3";
> + r->ctrl_scope = RESCTRL_L3_CACHE;
> + }
> +
> + /*
> + * Which bits are shared with other ...things...
> + * Unknown devices use partid-0 which uses all the bitmap
> + * fields. Until we configured the SMMU and GIC not to do this
> + * 'all the bits' is the correct answer here.
> + */
> + r->cache.shareable_bits = resctrl_get_default_ctrl(r);

I would like to recommend one style change to set r->alloc_capable as the final
setting. This is the setting that informs resctrl fs that this resource needs
attention. The reason I recommend this to be done last is if/when a future
change adds some configuration here that may fail then it should not fail with
r->alloc_capable as true while partially initialized.

> + break;
> + default:
> + return -EINVAL;
> + }
>
> return 0;
> }
> @@ -324,7 +409,8 @@ int mpam_resctrl_setup(void)
> res->resctrl_res.rid = rid;
> }
>
> - /* TODO: pick MPAM classes to map to resctrl resources */
> + /* Find some classes to use for controls */
> + mpam_resctrl_pick_caches();
>
> /* Initialise the resctrl structures from the classes */
> for_each_mpam_resctrl_control(res, rid) {

Reinette