[PATCH 17/19] 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/builtin-ftrace.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 8d04e5afe2d3..d376b37c53fc 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -49,6 +49,7 @@ struct perf_ftrace {
 	bool			trace_children;
 	unsigned		buffer_size_kb;
 	bool			no_pager;
+	unsigned		initial_delay;
 };
 
 struct filter_entry {
@@ -617,13 +618,23 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
 	/* display column headers */
 	read_tracing_file_to_stdout("trace");
 
-	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;
@@ -747,6 +758,8 @@ int cmd_ftrace(int argc, const char **argv)
 		     "size of per cpu buffer in kb"),
 	OPT_BOOLEAN('P', "no-pager", &ftrace.no_pager,
 		    "Do not use pager"),
+	OPT_UINTEGER('d', "delay", &ftrace.initial_delay,
+		     "Wait <n> ms before tracing"),
 	OPT_END()
 	};
 
-- 
2.25.1