[PATCH] perf ftrace latency: Do not read trace files when BPF is used

[Namhyung Kim <namhyung@kernel.org>]

I've realized that it didn't set up the tracing files when BPF is used
so poll() just returns immediately.  It ends up with calling poll()
unnecessarily in a loop.

BPF still needs the loop to wait for the target process exiting or a
signal from users.  Let's sleep for 1 msec and check that.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-ftrace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 4f881a40c311ae52..e61b9de11e1e41c7 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -1146,6 +1146,11 @@ static int __cmd_latency(struct perf_ftrace *ftrace)
 
 	line[0] = '\0';
 	while (!done) {
+		if (ftrace->target.use_bpf) {
+			usleep(1000);
+			continue;
+		}
+
 		if (poll(&pollfd, 1, -1) < 0)
 			break;
 
-- 
2.55.0.897.gb25b4bd76c-goog