[PATCH RFC v6 14/18] riscv_cbqri: resctrl: Add MB_WGHT bandwidth allocation via Mweight

[Drew Fustini]

Add bandwidth allocation through Mweight (shared weight for unreserved
bandwidth) exposed as the MB_WGHT resource. Mweight has no MBA
equivalent, so it lands as a new RDT_RESOURCE_*.

Mweight is an integer in [0, 255]. A value of 0 disables work-
conserving sharing for the group, capping its bandwidth at the
MB_MIN reservation. Values 1..255 compete for the leftover pool in
proportion to the weight.

The same BC backs both MB_MIN and MB_WGHT and bc_bw_alloc packs Rbwb and
Mweight in one register. cbqri_attach_cpu_to_bw_ctrl() attaches both
rids to the picked BC.

Reset gives every RCID the new-group default (max_bw = 255) for
equal opportunistic shares.

Assisted-by: Claude:claude-opus-4-7
Co-developed-by: Adrien Ricciardi <aricciardi@xxxxxxxxxxxx>
Signed-off-by: Adrien Ricciardi <aricciardi@xxxxxxxxxxxx>
Signed-off-by: Drew Fustini <fustini@xxxxxxxxxx>
---
 drivers/resctrl/cbqri_resctrl.c | 90 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 86 insertions(+), 4 deletions(-)

diff --git a/drivers/resctrl/cbqri_resctrl.c b/drivers/resctrl/cbqri_resctrl.c
index 1d312004b07d..14b955eb7949 100644
--- a/drivers/resctrl/cbqri_resctrl.c
+++ b/drivers/resctrl/cbqri_resctrl.c
@@ -366,6 +366,8 @@ int resctrl_arch_update_one(struct rdt_resource *r, struct rdt_ctrl_domain *d,
 	case RDT_RESOURCE_MB_MIN:
 		/* sum(Rbwb) <= MRBWB validation runs inside cbqri_apply_rbwb(). */
 		return cbqri_apply_rbwb(dom->hw_ctrl, closid, cfg_val, true);
+	case RDT_RESOURCE_MB_WGHT:
+		return cbqri_apply_mweight_config(dom->hw_ctrl, closid, cfg_val);
 	default:
 		return -EINVAL;
 	}
@@ -426,6 +428,14 @@ u32 resctrl_arch_get_config(struct rdt_resource *r, struct rdt_ctrl_domain *d,
 			val = (u32)rbwb;
 		break;
 	}
+	case RDT_RESOURCE_MB_WGHT: {
+		u64 mweight;
+
+		err = cbqri_read_mweight(ctrl, closid, &mweight);
+		if (err == 0)
+			val = (u32)mweight;
+		break;
+	}
 	default:
 		break;
 	}
@@ -485,6 +495,18 @@ void resctrl_arch_reset_all_ctrls(struct rdt_resource *r)
 							   rcid, rerr);
 			}
 			break;
+		case RDT_RESOURCE_MB_WGHT:
+			/* All RCIDs start at max weight (the new-group default). */
+			for (i = 0; i < hw_res->ctrl->rcid_count; i++) {
+				int rerr;
+
+				rerr = cbqri_apply_mweight_config(dom->hw_ctrl, i,
+								  default_ctrl);
+				if (rerr)
+					pr_err_ratelimited("Mweight reset RCID %u failed (%d)\n",
+							   i, rerr);
+			}
+			break;
 		default:
 			for (i = 0; i < hw_res->ctrl->rcid_count; i++) {
 				for (t = 0; t < CDP_NUM_TYPES; t++) {
@@ -549,6 +571,11 @@ static int cbqri_init_domain_ctrlval(struct rdt_resource *r, struct rdt_ctrl_dom
 
 			err = cbqri_apply_rbwb(dom->hw_ctrl, rcid, rbwb, false);
 			break;
+		case RDT_RESOURCE_MB_WGHT:
+			/* Match the new-group default: equal weights across RCIDs. */
+			err = cbqri_apply_mweight_config(dom->hw_ctrl, i,
+							 resctrl_get_default_ctrl(r));
+			break;
 		default:
 			/*
 			 * Seed both DATA and CODE staged slots so a later
@@ -690,6 +717,25 @@ static int cbqri_resctrl_control_init(struct cbqri_resctrl_res *cbqri_res)
 		INIT_LIST_HEAD(&res->mon_domains);
 		break;
 
+	case RDT_RESOURCE_MB_WGHT:
+		res->name = "MB_WGHT";
+		res->schema_fmt = RESCTRL_SCHEMA_RANGE;
+		res->ctrl_scope = RESCTRL_L3_CACHE;
+		/* Mweight is a dimensionless ratio. No delay/linear concept. */
+		res->membw.throttle_mode = THREAD_THROTTLE_UNDEFINED;
+		/*
+		 * CBQRI section 4.5: Mweight is 0-255 (0 disables
+		 * work-conserving). No sum constraint, so leave
+		 * default_to_min false. Groups default to max_bw.
+		 */
+		res->membw.min_bw = 0;
+		res->membw.max_bw = 255;
+		res->membw.bw_gran = 1;
+		res->alloc_capable = ctrl->alloc_capable;
+		INIT_LIST_HEAD(&res->ctrl_domains);
+		INIT_LIST_HEAD(&res->mon_domains);
+		break;
+
 	default:
 		break;
 	}
@@ -698,13 +744,12 @@ static int cbqri_resctrl_control_init(struct cbqri_resctrl_res *cbqri_res)
 }
 
 /*
- * Pick one BC to back MB_MIN.  Multiple BCs must agree on rcid_count
- * and mrbwb.  Mismatch is fatal because resctrl exposes a single set
- * of caps per rid.
+ * Pick one BC to back both MB_MIN and MB_WGHT.
  */
 static int cbqri_resctrl_pick_bw_alloc(void)
 {
 	struct cbqri_resctrl_res *mb_min = &cbqri_resctrl_resources[RDT_RESOURCE_MB_MIN];
+	struct cbqri_resctrl_res *mb_wght = &cbqri_resctrl_resources[RDT_RESOURCE_MB_WGHT];
 	struct cbqri_controller *ctrl;
 
 	list_for_each_entry(ctrl, &cbqri_controllers, list) {
@@ -723,6 +768,7 @@ static int cbqri_resctrl_pick_bw_alloc(void)
 		}
 
 		mb_min->ctrl = ctrl;
+		mb_wght->ctrl = ctrl;
 	}
 
 	return 0;
@@ -961,10 +1007,46 @@ static int cbqri_attach_cpu_to_one_bw_res(struct cbqri_controller *ctrl,
 	return 0;
 }
 
+static void cbqri_detach_cpu_from_one_bw_res(struct cbqri_controller *ctrl,
+					     enum resctrl_res_level rid,
+					     unsigned int cpu)
+{
+	struct cbqri_resctrl_res *hw_res = &cbqri_resctrl_resources[rid];
+	struct rdt_resource *res = &hw_res->resctrl_res;
+	struct rdt_ctrl_domain *domain;
+	int dom_id = ctrl->mem.prox_dom;
+
+	lockdep_assert_held(&cbqri_domain_list_lock);
+
+	if (!hw_res->ctrl)
+		return;
+
+	domain = cbqri_find_ctrl_domain(&res->ctrl_domains, dom_id);
+	if (!domain || !cpumask_test_cpu(cpu, &domain->hdr.cpu_mask))
+		return;
+
+	cpumask_clear_cpu(cpu, &domain->hdr.cpu_mask);
+	if (cpumask_empty(&domain->hdr.cpu_mask)) {
+		resctrl_offline_ctrl_domain(res, domain);
+		list_del(&domain->hdr.list);
+		kfree(container_of(domain, struct cbqri_resctrl_dom,
+				   resctrl_ctrl_dom));
+	}
+}
+
 static int cbqri_attach_cpu_to_bw_ctrl(struct cbqri_controller *ctrl,
 				       unsigned int cpu)
 {
-	return cbqri_attach_cpu_to_one_bw_res(ctrl, RDT_RESOURCE_MB_MIN, cpu);
+	int err;
+
+	err = cbqri_attach_cpu_to_one_bw_res(ctrl, RDT_RESOURCE_MB_MIN, cpu);
+	if (err)
+		return err;
+
+	err = cbqri_attach_cpu_to_one_bw_res(ctrl, RDT_RESOURCE_MB_WGHT, cpu);
+	if (err)
+		cbqri_detach_cpu_from_one_bw_res(ctrl, RDT_RESOURCE_MB_MIN, cpu);
+	return err;
 }
 
 static void cbqri_detach_cpu_from_l3_mon(struct rdt_resource *res,

-- 
2.43.0