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From:   Tony Luck <tony.luck@intel.com>
To:     Fenghua Yu <fenghua.yu@intel.com>,
        Reinette Chatre <reinette.chatre@intel.com>,
        Peter Newman <peternewman@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <skhan@linuxfoundation.org>, x86@kernel.org
Cc:     Shaopeng Tan <tan.shaopeng@fujitsu.com>,
        James Morse <james.morse@arm.com>,
        Jamie Iles <quic_jiles@quicinc.com>,
        Babu Moger <babu.moger@amd.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        patches@lists.linux.dev, Tony Luck <tony.luck@intel.com>
Subject: [PATCH v3] x86/resctrl: mba_MBps: Fall back to total b/w if local b/w unavailable
Date:   Thu, 26 Oct 2023 13:02:14 -0700
Message-ID: <20231026200214.16017-1-tony.luck@intel.com>
In-Reply-To: <20231025235046.12940-1-tony.luck@intel.com>
References: <20231025235046.12940-1-tony.luck@intel.com>
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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@intel.com>
---
Change since v2:

Babu doesn't like the global variable. So here's a version without it.

Note that my preference is still the v2 version. But as I tell newbies
to Linux "Your job isn't to get YOUR patch upstream. You job is to get
the problem fixed.".  So taking my own advice I don't really mind
whether v2 or v3 is applied.

 arch/x86/kernel/cpu/resctrl/monitor.c  | 43 ++++++++++++++++++--------
 arch/x86/kernel/cpu/resctrl/rdtgroup.c |  2 +-
 2 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index f136ac046851..29e86310677d 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -418,6 +418,20 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
 	return 0;
 }
 
+/*
+ * For legacy compatibility use the local memory bandwidth to drive
+ * the mba_MBps feedback control loop. But on platforms that do not
+ * provide the local event fall back to use the total bandwidth event
+ * instead.
+ */
+static enum resctrl_event_id pick_mba_mbps_event(void)
+{
+	if (is_mbm_local_enabled())
+		return QOS_L3_MBM_LOCAL_EVENT_ID;
+
+	return QOS_L3_MBM_TOTAL_EVENT_ID;
+}
+
 /*
  * mbm_bw_count() - Update bw count from values previously read by
  *		    __mon_event_count().
@@ -431,9 +445,11 @@ 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];
+	enum resctrl_event_id mba_mbps_evt_id = pick_mba_mbps_event();
 	u64 cur_bw, bytes, cur_bytes;
+	struct mbm_state *m;
 
+	m = get_mbm_state(rr->d, rmid, mba_mbps_evt_id);
 	cur_bytes = rr->val;
 	bytes = cur_bytes - m->prev_bw_bytes;
 	m->prev_bw_bytes = cur_bytes;
@@ -518,6 +534,7 @@ void mon_event_count(void *info)
  */
 static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 {
+	enum resctrl_event_id mba_mbps_evt_id = pick_mba_mbps_event();
 	u32 closid, rmid, cur_msr_val, new_msr_val;
 	struct mbm_state *pmbm_data, *cmbm_data;
 	u32 cur_bw, delta_bw, user_bw;
@@ -526,14 +543,14 @@ 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 +570,7 @@ 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 +612,7 @@ 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 +638,15 @@ 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);
 }
 
 /*
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