[RFC PATCH 1/1] smp: Add tracepoints for functions called with smp_call_function*()

[Leonardo Bras]

When running RT workloads in isolated CPUs, many cases of deadline misses
are caused by remote CPU requests such as smp_call_function*().

For those cases, having the names of those functions running around the
deadline miss moment could help finding a target for the next improvements.

Add tracepoints for acquiring the funtion name & argument before entry and
after exitting the called function.

Signed-off-by: Leonardo Bras <leobras@xxxxxxxxxx>
---
 include/trace/events/smp.h | 56 ++++++++++++++++++++++++++++++++++++++
 kernel/smp.c               | 11 ++++++++
 2 files changed, 67 insertions(+)
 create mode 100644 include/trace/events/smp.h

diff --git a/include/trace/events/smp.h b/include/trace/events/smp.h
new file mode 100644
index 0000000000000..94aae8d71705d
--- /dev/null
+++ b/include/trace/events/smp.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM smp
+
+#if !defined(_TRACE_SMP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SMP_H
+
+#include <linux/tracepoint.h>
+#include <linux/smp.h>
+
+/*
+ * Tracepoints for a function which is called as an effect of smp_call_function.*
+ */
+TRACE_EVENT(smp_call_function_entry,
+
+	TP_PROTO(smp_call_func_t func, void *info),
+
+	TP_ARGS(func, info),
+
+	TP_STRUCT__entry(
+		__field(void *,	func)
+		__field(void *,	info)
+	),
+
+	TP_fast_assign(
+		__entry->func	= func;
+		__entry->info	= info;
+	),
+
+	TP_printk("function %ps, argument = %p", __entry->func, __entry->info)
+);
+
+
+TRACE_EVENT(smp_call_function_exit,
+
+	TP_PROTO(smp_call_func_t func, void *info),
+
+	TP_ARGS(func, info),
+
+	TP_STRUCT__entry(
+		__field(void *,	func)
+		__field(void *,	info)
+	),
+
+	TP_fast_assign(
+		__entry->func	= func;
+		__entry->info	= info;
+	),
+
+	TP_printk("function %ps with argument = %p", __entry->func, __entry->info)
+);
+
+#endif /* _TRACE_SMP_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/smp.c b/kernel/smp.c
index 06a413987a14a..38d8dec28c39c 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -29,6 +29,9 @@
 #include "smpboot.h"
 #include "sched/smp.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/smp.h>
+
 #define CSD_TYPE(_csd)	((_csd)->node.u_flags & CSD_FLAG_TYPE_MASK)
 
 #ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
@@ -517,7 +520,9 @@ static int generic_exec_single(int cpu, struct __call_single_data *csd)
 		csd_lock_record(csd);
 		csd_unlock(csd);
 		local_irq_save(flags);
+		trace_smp_call_function_entry(func, info);
 		func(info);
+		trace_smp_call_function_exit(func, info);
 		csd_lock_record(NULL);
 		local_irq_restore(flags);
 		return 0;
@@ -627,7 +632,9 @@ static void __flush_smp_call_function_queue(bool warn_cpu_offline)
 			}
 
 			csd_lock_record(csd);
+			trace_smp_call_function_entry(func, info);
 			func(info);
+			trace_smp_call_function_exit(func, info);
 			csd_unlock(csd);
 			csd_lock_record(NULL);
 		} else {
@@ -662,7 +669,9 @@ static void __flush_smp_call_function_queue(bool warn_cpu_offline)
 
 				csd_lock_record(csd);
 				csd_unlock(csd);
+				trace_smp_call_function_entry(func, info);
 				func(info);
+				trace_smp_call_function_exit(func, info);
 				csd_lock_record(NULL);
 			} else if (type == CSD_TYPE_IRQ_WORK) {
 				irq_work_single(csd);
@@ -975,7 +984,9 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
 		unsigned long flags;
 
 		local_irq_save(flags);
+		trace_smp_call_function_entry(func, info);
 		func(info);
+		trace_smp_call_function_exit(func, info);
 		local_irq_restore(flags);
 	}
 
-- 
2.40.0