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Date:   Wed, 25 Oct 2023 16:50:46 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Peter Newman <peternewman@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, x86@...nel.org
Cc:     Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Babu Moger <babu.moger@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        patches@...ts.linux.dev, Tony Luck <tony.luck@...el.com>
Subject: [PATCH v2] x86/resctrl: mba_MBps: Fall back to total b/w if local b/w unavailable

On Intel the various resource director technology (RDT) features are all
orthogonal and independently enumerated. Thus it is possible to have
a system that  provides "total" memory bandwidth measurements without
providing "local" bandwidth measurements.

If local bandwidth measurement is not available, do not give up on
providing the "mba_MBps" feedback option completely, make the code fall
back to using total bandwidth.

Signed-off-by: Tony Luck <tony.luck@...el.com>
---

Changes since v1:

+ Both Peter and Babu didn't like my get_mbm_data() function. Peter
  thought it just needed a more descriptive name. But Babu explained
  how to get rid of it completley. I went with a modified version of
  Babu's suggestion (saving the event to use for mba_MBps during
  initialization, instead of checking every time).

 arch/x86/kernel/cpu/resctrl/monitor.c  | 41 ++++++++++++++++----------
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  2 +-
 2 files changed, 27 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index f136ac046851..6c3536af024e 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -73,6 +73,13 @@ unsigned int resctrl_rmid_realloc_threshold;
  */
 unsigned int resctrl_rmid_realloc_limit;
 
+/*
+ * MBM monitor event to use for the mba_MBps mount option.
+ * Preference is QOS_L3_MBM_LOCAL_EVENT_ID, but fall
+ * back to QOS_L3_MBM_TOTAL_EVENT_ID.
+ */
+static enum resctrl_event_id mba_mbps_evt_id;
+
 #define CF(cf)	((unsigned long)(1048576 * (cf) + 0.5))
 
 /*
@@ -431,7 +438,7 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
  */
 static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
 {
-	struct mbm_state *m = &rr->d->mbm_local[rmid];
+	struct mbm_state *m = get_mbm_state(rr->d, rmid, mba_mbps_evt_id);
 	u64 cur_bw, bytes, cur_bytes;
 
 	cur_bytes = rr->val;
@@ -526,14 +533,14 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 	struct list_head *head;
 	struct rdtgroup *entry;
 
-	if (!is_mbm_local_enabled())
+	if (!is_mbm_enabled())
 		return;
 
 	r_mba = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
 
 	closid = rgrp->closid;
 	rmid = rgrp->mon.rmid;
-	pmbm_data = &dom_mbm->mbm_local[rmid];
+	pmbm_data = get_mbm_state(dom_mbm, rmid, mba_mbps_evt_id);
 
 	dom_mba = get_domain_from_cpu(smp_processor_id(), r_mba);
 	if (!dom_mba) {
@@ -553,7 +560,7 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 	 */
 	head = &rgrp->mon.crdtgrp_list;
 	list_for_each_entry(entry, head, mon.crdtgrp_list) {
-		cmbm_data = &dom_mbm->mbm_local[entry->mon.rmid];
+		cmbm_data = get_mbm_state(dom_mbm, entry->mon.rmid, mba_mbps_evt_id);
 		cur_bw += cmbm_data->prev_bw;
 		delta_bw += cmbm_data->delta_bw;
 	}
@@ -595,7 +602,7 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 	 */
 	pmbm_data->delta_comp = true;
 	list_for_each_entry(entry, head, mon.crdtgrp_list) {
-		cmbm_data = &dom_mbm->mbm_local[entry->mon.rmid];
+		cmbm_data = get_mbm_state(dom_mbm, entry->mon.rmid, mba_mbps_evt_id);
 		cmbm_data->delta_comp = true;
 	}
 }
@@ -621,15 +628,15 @@ static void mbm_update(struct rdt_resource *r, struct rdt_domain *d, int rmid)
 		rr.evtid = QOS_L3_MBM_LOCAL_EVENT_ID;
 		rr.val = 0;
 		__mon_event_count(rmid, &rr);
-
-		/*
-		 * Call the MBA software controller only for the
-		 * control groups and when user has enabled
-		 * the software controller explicitly.
-		 */
-		if (is_mba_sc(NULL))
-			mbm_bw_count(rmid, &rr);
 	}
+
+	/*
+	 * Call the MBA software controller only for the
+	 * control groups and when user has enabled
+	 * the software controller explicitly.
+	 */
+	if (is_mba_sc(NULL))
+		mbm_bw_count(rmid, &rr);
 }
 
 /*
@@ -769,10 +776,14 @@ static void l3_mon_evt_init(struct rdt_resource *r)
 
 	if (is_llc_occupancy_enabled())
 		list_add_tail(&llc_occupancy_event.list, &r->evt_list);
-	if (is_mbm_total_enabled())
+	if (is_mbm_total_enabled()) {
 		list_add_tail(&mbm_total_event.list, &r->evt_list);
-	if (is_mbm_local_enabled())
+		mba_mbps_evt_id = QOS_L3_MBM_TOTAL_EVENT_ID;
+	}
+	if (is_mbm_local_enabled()) {
 		list_add_tail(&mbm_local_event.list, &r->evt_list);
+		mba_mbps_evt_id = QOS_L3_MBM_LOCAL_EVENT_ID;
+	}
 }
 
 int __init rdt_get_mon_l3_config(struct rdt_resource *r)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 69a1de92384a..0c4f8a1b8df0 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2294,7 +2294,7 @@ static bool supports_mba_mbps(void)
 {
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
 
-	return (is_mbm_local_enabled() &&
+	return (is_mbm_enabled() &&
 		r->alloc_capable && is_mba_linear());
 }
 
-- 
2.41.0

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