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

Ben Horgan
2026-02-11T11:05:38Z

Hi Reinette,

On Tue, Feb 10, 2026 at 03:39:51PM -0800, Reinette Chatre wrote:
> 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.

Yes, not ideal but I don't think it's urgent to tidy this up.

>
> > + 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.

Makes sense. This will make the code more robust.

>
> > + 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

Thanks,

Ben