[PATCH v3 04/17] perf ftrace: add option -d/--delay to delay tracing

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

This adds an option '-d/--delay' to allow us to start tracing some
times later after workload is launched.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
---
 tools/perf/Documentation/perf-ftrace.txt |  4 ++++
 tools/perf/builtin-ftrace.c              | 19 ++++++++++++++++---
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
index e204bf6d50d8..fd1776deebd7 100644
--- a/tools/perf/Documentation/perf-ftrace.txt
+++ b/tools/perf/Documentation/perf-ftrace.txt
@@ -42,6 +42,10 @@ OPTIONS
 --tid=::
 	Trace on existing thread id (comma separated list).
 
+-d::
+--delay::
+	Time (ms) to wait before starting tracing after program start.
+
 -a::
 --all-cpus::
 	Force system-wide collection.  Scripts run without a <command>
diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 1188b82c6541..7793c3d083e0 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -38,6 +38,7 @@ struct perf_ftrace {
 	struct list_head	graph_funcs;
 	struct list_head	nograph_funcs;
 	int			graph_depth;
+	unsigned		initial_delay;
 };
 
 struct filter_entry {
@@ -402,13 +403,23 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 	fcntl(trace_fd, F_SETFL, O_NONBLOCK);
 	pollfd.fd = trace_fd;
 
-	if (write_tracing_file("tracing_on", "1") < 0) {
-		pr_err("can't enable tracing\n");
-		goto out_close_fd;
+	if (!ftrace->initial_delay) {
+		if (write_tracing_file("tracing_on", "1") < 0) {
+			pr_err("can't enable tracing\n");
+			goto out_close_fd;
+		}
 	}
 
 	perf_evlist__start_workload(ftrace->evlist);
 
+	if (ftrace->initial_delay) {
+		usleep(ftrace->initial_delay * 1000);
+		if (write_tracing_file("tracing_on", "1") < 0) {
+			pr_err("can't enable tracing\n");
+			goto out_close_fd;
+		}
+	}
+
 	while (!done) {
 		if (poll(&pollfd, 1, -1) < 0)
 			break;
@@ -535,6 +546,8 @@ int cmd_ftrace(int argc, const char **argv)
 		     "Set nograph filter on given functions", parse_filter_func),
 	OPT_INTEGER('D', "graph-depth", &ftrace.graph_depth,
 		    "Max depth for function graph tracer"),
+	OPT_UINTEGER('d', "delay", &ftrace.initial_delay,
+		     "ms to wait before starting tracing after program start"),
 	OPT_END()
 	};
 
-- 
2.25.1