[PATCH v2 06/15] 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>
---
 tools/perf/Documentation/perf-ftrace.txt |  4 ++++
 tools/perf/builtin-ftrace.c              | 22 ++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
index fd1776deebd7..a18d640e90bb 100644
--- a/tools/perf/Documentation/perf-ftrace.txt
+++ b/tools/perf/Documentation/perf-ftrace.txt
@@ -60,6 +60,10 @@ 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 in KB.
+
 -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 003efa756322..e45496012611 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -39,6 +39,7 @@ struct perf_ftrace {
 	struct list_head	nograph_funcs;
 	int			graph_depth;
 	unsigned		initial_delay;
+	unsigned		buffer_size_kb;
 };
 
 struct filter_entry {
@@ -321,6 +322,20 @@ static int set_tracing_depth(struct perf_ftrace *ftrace)
 	return 0;
 }
 
+static int set_tracing_buffer_size_kb(struct perf_ftrace *ftrace)
+{
+	int ret;
+
+	if (ftrace->buffer_size_kb == 0)
+		return 0;
+
+	ret = write_tracing_file_int("buffer_size_kb", ftrace->buffer_size_kb);
+	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 +400,11 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 		goto out_reset;
 	}
 
+	if (set_tracing_buffer_size_kb(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;
@@ -555,6 +575,8 @@ 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_UINTEGER('m', "buffer-size", &ftrace.buffer_size_kb,
+		     "size of per cpu buffer in kb"),
 	OPT_END()
 	};
 
-- 
2.25.1