[PATCH v14 11/24] fs/resctrl: Add interface to disable a monitor event

[Tony Luck]

resctrl assumes that every monitor event is enabled before any domain is
created, since domains are created from CPU hotplug callbacks and their
per-domain state depends on the events enabled at that time. Events, once
enabled, stay enabled.

resctrl enumerates Application Energy Telemetry (AET) events from data provided
by the pmt_telemetry driver, which currently must be built in. Allowing the
driver to be a loadable module means AET events must be enumerated on every
mount and disabled again on unmount, so the driver can be unloaded while
resctrl is not mounted. There is no way to disable an event.

Add resctrl_disable_mon_event(). The architecture owns domain lifetime, so
it is responsible for calling this only while resctrl is unmounted and for
cleaning up any per-domain state. These requirements are not enforced in
code, so document them in kerneldoc, alongside the matching requirements
for enabling an event.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
v14:
	New commit message. Dropped previous applied Reinette RB tag.
---
 include/linux/resctrl.h | 36 ++++++++++++++++++++++++++++++++++++
 fs/resctrl/monitor.c    | 15 +++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 0e7fce070fde..764c45be2d59 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -449,9 +449,45 @@ u32 resctrl_arch_get_num_closid(struct rdt_resource *r);
 u32 resctrl_arch_system_num_rmid_idx(void);
 int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);
 
+/**
+ * resctrl_enable_mon_event() - Enable monitoring event
+ * @eventid:	ID of the event.
+ * @any_cpu:	True if event data can be read from any CPU.
+ * @binary_bits: Number of binary places of the fixed-point value expected to
+ *		back a floating point event. Can only be set for floating point
+ *		events.
+ * @arch_priv:	Architecture private data associated with event. Passed back to
+ *		architecture when reading the event via resctrl_arch_rmid_read().
+ *
+ * The file system must not be mounted when enabling an event.
+ *
+ * Events that require per-domain (architectural and/or filesystem) state must
+ * be enabled before the domain structures are allocated. For example before
+ * CPU hotplug callbacks that allocate domain structures are registered. If the
+ * architecture discovers a resource after initialization it should enable
+ * events needing per-domain state before any domain structure allocation which
+ * should be coordinated with the CPU hotplug callbacks.
+ *
+ * Return:
+ * true if event was successfully enabled, false otherwise.
+ */
 bool resctrl_enable_mon_event(enum resctrl_event_id eventid, bool any_cpu,
 			      unsigned int binary_bits, void *arch_priv);
 
+/**
+ * resctrl_disable_mon_event() - Disable monitoring event
+ * @eventid:	ID of the event
+ *
+ * Never disable an event while the file system is mounted. Never
+ * disable an event that may be accessed while the file system is
+ * unmounted.
+ *
+ * Events that require per-domain (architectural and/or filesystem) state
+ * will require additional cleanup which should be coordinated with the CPU
+ * hotplug callbacks.
+ */
+void resctrl_disable_mon_event(enum resctrl_event_id eventid);
+
 bool resctrl_is_mon_event_enabled(enum resctrl_event_id eventid);
 
 bool resctrl_arch_is_evt_configurable(enum resctrl_event_id evt);
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index f05be52ab5b3..fbbb31e9618b 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1068,6 +1068,21 @@ bool resctrl_enable_mon_event(enum resctrl_event_id eventid, bool any_cpu,
 	return true;
 }
 
+void resctrl_disable_mon_event(enum resctrl_event_id eventid)
+{
+	if (WARN_ON_ONCE(eventid < QOS_FIRST_EVENT || eventid >= QOS_NUM_EVENTS))
+		return;
+	if (!mon_event_all[eventid].enabled) {
+		pr_warn("Event %d already disabled\n", eventid);
+		return;
+	}
+
+	mon_event_all[eventid].any_cpu = false;
+	mon_event_all[eventid].binary_bits = 0;
+	mon_event_all[eventid].arch_priv = NULL;
+	mon_event_all[eventid].enabled = false;
+}
+
 bool resctrl_is_mon_event_enabled(enum resctrl_event_id eventid)
 {
 	return eventid >= QOS_FIRST_EVENT && eventid < QOS_NUM_EVENTS &&
-- 
2.56.0