[PATCH v3 06/17] perf ftrace: add option '-m/--buffer-size' to set per-cpu buffer size

[Changbin Du <changbin.du@gmail.com>]

This adds an option '-m/--buffer-size' to allow us set the size of per-cpu
tracing buffer.

Signed-off-by: Changbin Du <changbin.du@gmail.com>

---
v2: support units as a suffix.
---
 tools/perf/Documentation/perf-ftrace.txt |  5 +++
 tools/perf/builtin-ftrace.c              | 56 +++++++++++++++++++++++-
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
index fd1776deebd7..a26593dbdd76 100644
--- a/tools/perf/Documentation/perf-ftrace.txt
+++ b/tools/perf/Documentation/perf-ftrace.txt
@@ -60,6 +60,11 @@ OPTIONS
 	Ranges of CPUs are specified with -: 0-2.
 	Default is to trace on all online CPUs.
 
+-m::
+--buffer-size::
+	Set the size of per-cpu tracing buffer, <size> is expected to
+	be a number with appended unit character - B/K/M/G.
+
 -T::
 --trace-funcs=::
 	Only trace functions given by the argument.  Multiple functions
diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 7eb41f7027c8..66cdfe42b1fe 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -26,7 +26,7 @@
 #include "thread_map.h"
 #include "util/cap.h"
 #include "util/config.h"
-
+#include "util/units.h"
 
 struct perf_ftrace {
 	struct evlist		*evlist;
@@ -39,6 +39,7 @@ struct perf_ftrace {
 	struct list_head	nograph_funcs;
 	int			graph_depth;
 	unsigned		initial_delay;
+	unsigned long		percpu_buffer_size;
 };
 
 struct filter_entry {
@@ -321,6 +322,21 @@ static int set_tracing_depth(struct perf_ftrace *ftrace)
 	return 0;
 }
 
+static int set_tracing_percpu_buffer_size(struct perf_ftrace *ftrace)
+{
+	int ret;
+
+	if (ftrace->percpu_buffer_size == 0)
+		return 0;
+
+	ret = write_tracing_file_int("buffer_size_kb",
+				     ftrace->percpu_buffer_size / 1024);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
 static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 {
 	char *trace_file;
@@ -385,6 +401,11 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 		goto out_reset;
 	}
 
+	if (set_tracing_percpu_buffer_size(ftrace) < 0) {
+		pr_err("failed to set tracing per-cpu buffer size\n");
+		goto out_reset;
+	}
+
 	if (write_tracing_file("current_tracer", ftrace->tracer) < 0) {
 		pr_err("failed to set current_tracer to %s\n", ftrace->tracer);
 		goto out_reset;
@@ -514,6 +535,37 @@ static void delete_filter_func(struct list_head *head)
 	}
 }
 
+static int parse_buffer_size(const struct option *opt,
+			     const char *str, int unset)
+{
+	unsigned long *s = (unsigned long *)opt->value;
+	static struct parse_tag tags_size[] = {
+		{ .tag  = 'B', .mult = 1       },
+		{ .tag  = 'K', .mult = 1 << 10 },
+		{ .tag  = 'M', .mult = 1 << 20 },
+		{ .tag  = 'G', .mult = 1 << 30 },
+		{ .tag  = 0 },
+	};
+	unsigned long val;
+
+	if (unset) {
+		*s = 0;
+		return 0;
+	}
+
+	val = parse_tag_value(str, tags_size);
+	if (val != (unsigned long) -1) {
+		if (val < 1024) {
+			pr_err("buffer size too small, must larger than 1KB.");
+			return -1;
+		}
+		*s = val;
+		return 0;
+	}
+
+	return -1;
+}
+
 int cmd_ftrace(int argc, const char **argv)
 {
 	int ret;
@@ -555,6 +607,8 @@ int cmd_ftrace(int argc, const char **argv)
 		    "Max depth for function graph tracer"),
 	OPT_UINTEGER('d', "delay", &ftrace.initial_delay,
 		     "ms to wait before starting tracing after program start"),
+	OPT_CALLBACK('m', "buffer-size", &ftrace.percpu_buffer_size, "size",
+		     "size of per cpu buffer", parse_buffer_size),
 	OPT_END()
 	};
 
-- 
2.25.1