[PATCH v12 16/26] x86/resctrl: Report 'Unassigned' for MBM events in mbm_cntr_assign mode

Babu Moger
2025-04-04T00:21:17Z

In mbm_cntr_assign mode, the hardware counter should be assigned to read
the MBM events.

Report 'Unassigned' in case the user attempts to read the events without
assigning the counter.

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v12: Updated the documentation for more clarity.

v11: Domain can be NULL with SNC support so moved the unassign check in
rdtgroup_mondata_show().

v10: Moved the code to check the assign state inside mon_event_read().
Fixed few text comments.

v9: Used is_mbm_event() to check the event type.
Minor user documentation update.

v8: Used MBM_EVENT_ARRAY_INDEX to get the index for the MBM event.
Documentation update to make the text generic.

v7: Moved the documentation under "mon_data".
Updated the text little bit.

v6: Added more explaination in the resctrl.rst
Added checks to detect "Unassigned" before reading RMID.

v5: New patch.
---
Documentation/arch/x86/resctrl.rst | 10 ++++++++++
arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 14 ++++++++++++++
arch/x86/kernel/cpu/resctrl/internal.h | 3 +++
arch/x86/kernel/cpu/resctrl/monitor.c | 4 ++--
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 2 +-
5 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index 44128fbda4fe..71ed1cfed33a 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -430,6 +430,16 @@ When monitoring is enabled all MON groups will also contain:
for the L3 cache they occupy). These are named "mon_sub_L3_YY"
where "YY" is the node number.

+ The mbm_cntr_assign mode offers "num_mbm_cntrs" number of counters
+ and allows users to assign a counter to mon_hw_id, event pair enabling
+ bandwidth monitoring for as long as the counter remains assigned.
+ The hardware will continue tracking the assigned mon_hw_id until
+ the user manually unassigns it, ensuring that counters are not reset
+ during this period. System may run out of assignable counters when
+ all the counters are already assigned. In that case, MBM event counters
+ will return 'Unassigned' when the event is read. Users must manually
+ assign a counter to read the events.
+
"mon_hw_id":
Available only with debug option. The identifier used by hardware
for the monitor group. On x86 this is the RMID.
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 0a0ac5f6112e..2225c40b8888 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -710,6 +710,18 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
goto out;
}
d = container_of(hdr, struct rdt_mon_domain, hdr);
+
+ /*
+ * Report 'Unassigned' if mbm_cntr_assign mode is enabled and
+ * counter is unassigned.
+ */
+ if (resctrl_arch_mbm_cntr_assign_enabled(r) &&
+ resctrl_is_mbm_event(evtid) &&
+ (mbm_cntr_get(r, d, rdtgrp, evtid) < 0)) {
+ rr.err = -ENOENT;
+ goto checkresult;
+ }
+
mon_event_read(&rr, r, d, rdtgrp, &d->hdr.cpu_mask, evtid, false);
}

@@ -719,6 +731,8 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
seq_puts(m, "Error\n");
else if (rr.err == -EINVAL)
seq_puts(m, "Unavailable\n");
+ else if (rr.err == -ENOENT)
+ seq_puts(m, "Unassigned\n");
else
seq_printf(m, "%llu\n", rr.val);

diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 13a2a9b064df..fbb045aec7e5 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -574,10 +574,13 @@ bool closid_allocated(unsigned int closid);
int resctrl_find_cleanest_closid(void);
void arch_mbm_evt_config_init(struct rdt_hw_mon_domain *hw_dom);
unsigned int mon_event_config_index_get(u32 evtid);
+bool resctrl_is_mbm_event(int e);
int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
struct rdtgroup *rdtgrp, enum resctrl_event_id evtid, u32 evt_cfg);
int resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
struct rdtgroup *rdtgrp, enum resctrl_event_id evtid, u32 evt_cfg);
+int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
+ struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);

#ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 84dcb227f84c..5e7970fd0a97 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -1492,8 +1492,8 @@ static int resctrl_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
return ret;
}

-static int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
- struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
+int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
+ struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
{
int cntr_id;

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 07792b45bd63..d84f47db4e43 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -123,7 +123,7 @@ static bool resctrl_is_mbm_enabled(void)
resctrl_arch_is_mbm_local_enabled());
}

-static bool resctrl_is_mbm_event(int e)
+bool resctrl_is_mbm_event(int e)
{
return (e >= QOS_L3_MBM_TOTAL_EVENT_ID &&
e <= QOS_L3_MBM_LOCAL_EVENT_ID);
--
2.34.1