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

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 use a semaphore instead.

Suggested-by: Ian Rogers <irogers@google.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 22 insertions, 6 deletions

diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
index 4f881a40c311..6017493ff179 100644
--- a/tools/perf/builtin-ftrace.c
+++ b/tools/perf/builtin-ftrace.c
@@ -6,23 +6,23 @@
  * Copyright (c) 2020  Changbin Du <changbin.du@gmail.com>, significant enhancement.
  */
 
-#include "builtin.h"
-
+#include <ctype.h>
 #include <errno.h>
-#include <unistd.h>
-#include <signal.h>
-#include <stdlib.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <math.h>
 #include <poll.h>
-#include <ctype.h>
+#include <semaphore.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
 #include <linux/capability.h>
 #include <linux/err.h>
 #include <linux/string.h>
 #include <linux/zalloc.h>
 #include <sys/stat.h>
 
+#include "builtin.h"
 #include "debug.h"
 #include <subcmd/pager.h>
 #include <subcmd/parse-options.h>
@@ -45,6 +45,7 @@
 
 static volatile sig_atomic_t workload_exec_errno;
 static volatile sig_atomic_t done;
+static sem_t sig_sem;
 
 static struct stats latency_stats;  /* for tracepoints */
 
@@ -53,6 +54,7 @@ static char tracing_instance[PATH_MAX];	/* Trace instance directory */
 static void sig_handler(int sig __maybe_unused)
 {
 	done = true;
+	sem_post(&sig_sem);
 }
 
 /*
@@ -68,6 +70,7 @@ static void ftrace__workload_exec_failed_signal(int signo __maybe_unused,
 {
 	workload_exec_errno = info->si_value.sival_int;
 	done = true;
+	sem_post(&sig_sem);
 }
 
 static bool check_ftrace_capable(void)
@@ -1146,6 +1149,11 @@ static int __cmd_latency(struct perf_ftrace *ftrace)
 
 	line[0] = '\0';
 	while (!done) {
+		if (ftrace->target.use_bpf) {
+			sem_wait(&sig_sem);
+			break;
+		}
+
 		if (poll(&pollfd, 1, -1) < 0)
 			break;
 
@@ -1852,6 +1860,8 @@ int cmd_ftrace(int argc, const char **argv)
 	INIT_LIST_HEAD(&ftrace.nograph_funcs);
 	INIT_LIST_HEAD(&ftrace.event_pair);
 
+	sem_init(&sig_sem, 0, 0);
+
 	signal(SIGINT, sig_handler);
 	signal(SIGUSR1, sig_handler);
 	signal(SIGCHLD, sig_handler);
@@ -2015,5 +2025,11 @@ out_delete_filters:
 	delete_filter_func(&ftrace.nograph_funcs);
 	delete_filter_func(&ftrace.event_pair);
 
+	signal(SIGINT, SIG_DFL);
+	signal(SIGUSR1, SIG_DFL);
+	signal(SIGCHLD, SIG_DFL);
+	signal(SIGPIPE, SIG_DFL);
+
+	sem_destroy(&sig_sem);
 	return ret;
 }