linux-kernel - [PATCH] arch_topology: Trace the update thermal pressure

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Date:   Tue, 19 Apr 2022 17:48:01 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     linux-kernel@...r.kernel.org
Cc:     sudeep.holla@....com, dietmar.eggemann@....com,
        vincent.guittot@...aro.org, gregkh@...uxfoundation.org,
        rafael@...nel.org, rostedt@...dmis.org, mingo@...hat.com,
        lukasz.luba@....com
Subject: [PATCH] arch_topology: Trace the update thermal pressure

Add trace event to capture the moment of the call for updating the thermal
pressure value. It's helpful to investigate how often those events occurs
in a system dealing with throttling. This trace event is needed since the
old 'cdev_update' might not be used by some drivers. Also, the new trace
event shows capacity value, not a cooling state.

We already have a trace point 'pelt_thermal_tp' which after a change to
trace event can be paired with this new 'thermal_pressure_update' and
derive more insight what is going on in the system under pressure
(and why).

Signed-off-by: Lukasz Luba <lukasz.luba@....com>
---
 drivers/base/arch_topology.c   |  4 ++++
 include/trace/events/thermal.h | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 1d6636ebaac5..4f0392de3081 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -19,6 +19,8 @@
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
 
+#include <trace/events/thermal.h>
+
 static DEFINE_PER_CPU(struct scale_freq_data __rcu *, sft_data);
 static struct cpumask scale_freq_counters_mask;
 static bool scale_freq_invariant;
@@ -195,6 +197,8 @@ void topology_update_thermal_pressure(const struct cpumask *cpus,
 
 	th_pressure = max_capacity - capacity;
 
+	trace_thermal_pressure_update(cpu, th_pressure);
+
 	for_each_cpu(cpu, cpus)
 		WRITE_ONCE(per_cpu(thermal_pressure, cpu), th_pressure);
 }
diff --git a/include/trace/events/thermal.h b/include/trace/events/thermal.h
index 8a5f04888abd..1bf08ee1a25b 100644
--- a/include/trace/events/thermal.h
+++ b/include/trace/events/thermal.h
@@ -65,6 +65,25 @@ TRACE_EVENT(cdev_update,
 	TP_printk("type=%s target=%lu", __get_str(type), __entry->target)
 );
 
+TRACE_EVENT(thermal_pressure_update,
+
+	TP_PROTO(int cpu, unsigned long thermal_pressure),
+
+	TP_ARGS(cpu, thermal_pressure),
+
+	TP_STRUCT__entry(
+		__field(int, cpu)
+		__field(unsigned long, thermal_pressure)
+	),
+
+	TP_fast_assign(
+		__entry->cpu = cpu;
+		__entry->thermal_pressure = thermal_pressure;
+	),
+
+	TP_printk("cpu=%d thermal_pressure=%lu", __entry->cpu, __entry->thermal_pressure)
+);
+
 TRACE_EVENT(thermal_zone_trip,
 
 	TP_PROTO(struct thermal_zone_device *tz, int trip,
-- 
2.17.1