linux-kernel - [PATCH v2 1/5] tracing: Define new ftrace event "func

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Date:   Mon, 29 Mar 2021 16:05:29 +0300
From:   "Yordan Karadzhov (VMware)" <y.karadz@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     rostedt@...dmis.org, tglx@...utronix.de, peterz@...radead.org,
        "Yordan Karadzhov (VMware)" <y.karadz@...il.com>
Subject: [PATCH v2 1/5] tracing: Define new ftrace event "func_repeats"

The event aims to consolidate the function tracing record in the cases
when a single function is called number of times consecutively.

	while (cond)
		do_func();

This may happen in various scenarios (busy waiting for example).
The new ftrace event can be used to show repeated function events with
a single event and save space on the ring buffer

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@...il.com>
---
 kernel/trace/trace.h         |  3 +++
 kernel/trace/trace_entries.h | 39 ++++++++++++++++++++++++++++++
 kernel/trace/trace_output.c  | 47 ++++++++++++++++++++++++++++++++++++
 3 files changed, 89 insertions(+)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 5506424eae2a..6a5b4c2a0fa7 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -45,6 +45,7 @@ enum trace_type {
 	TRACE_BPUTS,
 	TRACE_HWLAT,
 	TRACE_RAW_DATA,
+	TRACE_FUNC_REPEATS,
 
 	__TRACE_LAST_TYPE,
 };
@@ -442,6 +443,8 @@ extern void __ftrace_bad_type(void);
 			  TRACE_GRAPH_ENT);		\
 		IF_ASSIGN(var, ent, struct ftrace_graph_ret_entry,	\
 			  TRACE_GRAPH_RET);		\
+		IF_ASSIGN(var, ent, struct func_repeats_entry,		\
+			  TRACE_FUNC_REPEATS);				\
 		__ftrace_bad_type();					\
 	} while (0)
 
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index 4547ac59da61..6f98c3b4e4fa 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -338,3 +338,42 @@ FTRACE_ENTRY(hwlat, hwlat_entry,
 		 __entry->nmi_total_ts,
 		 __entry->nmi_count)
 );
+
+#define FUNC_REPEATS_GET_DELTA_TS(entry)					\
+(((u64)entry->top_delta_ts << 32) | entry->bottom_delta_ts)			\
+
+#define FUNC_REPEATS_SET_DELTA_TS(entry, delta)					\
+	do {									\
+		if (likely(!((u64)delta >> 32))) {				\
+			entry->bottom_delta_ts = delta;				\
+			entry->top_delta_ts = 0;				\
+		} else {							\
+			if (likely(!((u64)delta >> 48))) {			\
+				entry->bottom_delta_ts = delta & U32_MAX;	\
+				entry->top_delta_ts = (delta >> 32);		\
+			} else {						\
+				/* Timestamp overflow. Set to max. */		\
+				entry->bottom_delta_ts = U32_MAX;		\
+				entry->top_delta_ts = U16_MAX;			\
+			}							\
+		}								\
+	} while (0);								\
+
+FTRACE_ENTRY(func_repeats, func_repeats_entry,
+
+	TRACE_FUNC_REPEATS,
+
+	F_STRUCT(
+		__field(	unsigned long,	ip		)
+		__field(	unsigned long,	parent_ip	)
+		__field(	u16	,	count		)
+		__field(	u16	,	top_delta_ts	)
+		__field(	u32	,	bottom_delta_ts	)
+	),
+
+	F_printk(" %ps <-%ps\t(repeats:%u  delta_ts: -%llu)",
+		 (void *)__entry->ip,
+		 (void *)__entry->parent_ip,
+		 __entry->count,
+		 FUNC_REPEATS_GET_DELTA_TS(__entry))
+);
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index a0146e1fffdf..55b08e146afc 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1373,6 +1373,52 @@ static struct trace_event trace_raw_data_event = {
 	.funcs		= &trace_raw_data_funcs,
 };
 
+static enum print_line_t
+trace_func_repeats_raw(struct trace_iterator *iter, int flags,
+			 struct trace_event *event)
+{
+	struct func_repeats_entry *field;
+	struct trace_seq *s = &iter->seq;
+
+	trace_assign_type(field, iter->ent);
+
+	trace_seq_printf(s, "%lu %lu %u %llu\n",
+			 field->ip,
+			 field->parent_ip,
+			 field->count,
+			 FUNC_REPEATS_GET_DELTA_TS(field));
+
+	return trace_handle_return(s);
+}
+
+static enum print_line_t
+trace_func_repeats_print(struct trace_iterator *iter, int flags,
+			 struct trace_event *event)
+{
+	struct func_repeats_entry *field;
+	struct trace_seq *s = &iter->seq;
+
+	trace_assign_type(field, iter->ent);
+
+	seq_print_ip_sym(s, field->ip, flags);
+	trace_seq_puts(s, " <-");
+	seq_print_ip_sym(s, field->parent_ip, flags);
+	trace_seq_printf(s, " (repeats: %u, delta_ts: -%llu)\n",
+			 field->count,
+			 FUNC_REPEATS_GET_DELTA_TS(field));
+
+	return trace_handle_return(s);
+}
+
+static struct trace_event_functions trace_func_repeats_funcs = {
+	.trace		= trace_func_repeats_print,
+	.raw		= trace_func_repeats_raw,
+};
+
+static struct trace_event trace_func_repeats_event = {
+	.type	 	= TRACE_FUNC_REPEATS,
+	.funcs		= &trace_func_repeats_funcs,
+};
 
 static struct trace_event *events[] __initdata = {
 	&trace_fn_event,
@@ -1385,6 +1431,7 @@ static struct trace_event *events[] __initdata = {
 	&trace_print_event,
 	&trace_hwlat_event,
 	&trace_raw_data_event,
+	&trace_func_repeats_event,
 	NULL
 };
 
-- 
2.25.1