Re: [PATCH v10 2/6] riscv_cbqri: resctrl: Add cache allocation via capacity block mask

[Drew Fustini <fustini@kernel.org>]

On Thu, Nov 05, 2026 at 04:05:29PM +0800, Zeng Heng wrote:
> Hi Drew,

Hi, thanks for reviewing.

> 在 11/5/26 上午12:35, Drew Fustini 写道:
> 
> ...
> 
> > +/*
> > + * Fill the rdt_resource fields for one picked rid. An rid with no picked
> > + * controller is left untouched so it stays out of resctrl_arch_get_resource().
> > + */
> > +static void cbqri_resctrl_control_init(struct cbqri_resctrl_res *cbqri_res)
> > +{
> > +	struct rdt_resource *res = &cbqri_res->resctrl_res;
> > +	struct cbqri_controller *ctrl;
> > +
> > +	if (!cbqri_res->nr_ctrls)
> > +		return;
> > +	ctrl = cbqri_res->ctrls[0];
> > +
> > +	switch (res->rid) {
> > +	case RDT_RESOURCE_L2:
> > +	case RDT_RESOURCE_L3:
> > +		res->name = (res->rid == RDT_RESOURCE_L2) ? "L2" : "L3";
> > +		res->schema_fmt = RESCTRL_SCHEMA_BITMAP;
> > +		res->ctrl_scope = (res->rid == RDT_RESOURCE_L2) ?
> > +				    RESCTRL_L2_CACHE : RESCTRL_L3_CACHE;
> > +		res->cache.cbm_len = ctrl->cc.ncblks;
> > +		res->cache.shareable_bits = 0;
> > +		res->cache.min_cbm_bits = 1;
> > +		res->cache.arch_has_sparse_bitmasks = false;
> 
> Currently, the driver sets arch_has_sparse_bitmasks to false, causing
> resctrl to require a contiguous bits in cache allocation masks. For
> example, L3:0=3 is accepted, whereas L3:0=11 is rejected because its
> set bits are non-contiguous.
> 
> The default should allow both contiguous and non-contiguous masks,
> provided they satisfy the other mask validity checks. A contiguity
> restriction should only be imposed when a specific hardware
> implementation can't support sparse masks explicitly.
> 
> So I propose enabling sparse cache allocation bitmasks by default.
> Thanks.

Good point, I will change arch_has_sparse_bitmasks to true. The spec
defines cc_block_mask as one bit per capacity block and there's no
contiguity requirement.

> > +		res->cdp_capable = ctrl->cc.supports_alloc_at_code;
> > +		res->alloc_capable = ctrl->alloc_capable;
> > +		INIT_LIST_HEAD(&res->ctrl_domains);
> > +		INIT_LIST_HEAD(&res->mon_domains);
> > +		break;
> > +	default:
> > +		break;
> > +	}
> > +}
> 
> Apart from this,
> 
> Reviewed-by: Zeng Heng <zengheng@picoheart.com>

Thanks!

Drew