[PATCH v1] trace-cmd: introduce --initital-delay for record command

[David Hildenbrand]

If recording a big number of events to a big buffer, one might want to
minimize the trace-cmd activity for a certain period in time.
Especially, don't see any trace-cmd activity for some time. If there are
a lot of events, the loop might actually never sleep, resulting in the
"-s" option never becomming active.

E.g. I am using scheduler events to trace thread activity per CPU. Esp.
sched:sched_wakeup and sched:sched_stat_runtime. Even when setting the
sleep time to something huge like 30 seconds, I can see constant activity
from the trace-cmd tasks.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 Documentation/trace-cmd-record.1.txt | 10 ++++++++++
 trace-cmd.h                          |  3 ++-
 trace-record.c                       | 11 ++++++++++-
 trace-recorder.c                     |  9 ++++++++-
 4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/Documentation/trace-cmd-record.1.txt b/Documentation/trace-cmd-record.1.txt
index 68afa16..d429caf 100644
--- a/Documentation/trace-cmd-record.1.txt
+++ b/Documentation/trace-cmd-record.1.txt
@@ -326,6 +326,16 @@ OPTIONS
     executed will not be changed. This is useful if you want to monitor the
     output of the command being executed, but not see the output from trace-cmd.
 
+*--initital-delay* 'delay'::
+    The processes that trace-cmd creates to record from the ring buffer need
+    to start copying the data from the ring buffer at some point in time.
+    Setting the 'delay' to zero will cause the processes to start copying
+    from the ring buffer immediately. This is helpful when wanting to
+    minimize trace-cmd activity during some period of time (where -s
+    will not help due to the amount of events being recorded).
+
+    The 'delay' metric is microseconds. The default is set to 0.
+
 EXAMPLES
 --------
 
diff --git a/trace-cmd.h b/trace-cmd.h
index 6fd34d7..bae7153 100644
--- a/trace-cmd.h
+++ b/trace-cmd.h
@@ -285,7 +285,8 @@ struct tracecmd_recorder *tracecmd_create_buffer_recorder_fd(int fd, int cpu, un
 struct tracecmd_recorder *tracecmd_create_buffer_recorder(const char *file, int cpu, unsigned flags, const char *buffer);
 struct tracecmd_recorder *tracecmd_create_buffer_recorder_maxkb(const char *file, int cpu, unsigned flags, const char *buffer, int maxkb);
 
-int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long sleep);
+int tracecmd_start_recording(struct tracecmd_recorder *recorder,
+			     unsigned long sleep, unsigned long initital_sleep);
 void tracecmd_stop_recording(struct tracecmd_recorder *recorder);
 void tracecmd_stat_cpu(struct trace_seq *s, int cpu);
 long tracecmd_flush_recording(struct tracecmd_recorder *recorder);
diff --git a/trace-record.c b/trace-record.c
index f128257..cd6e158 100644
--- a/trace-record.c
+++ b/trace-record.c
@@ -79,6 +79,7 @@ static const char *output_file = "trace.dat";
 
 static int latency;
 static int sleep_time = 1000;
+static int initial_sleep_time = 0;
 static int recorder_threads;
 static struct pid_record_data *pids;
 static int buffers;
@@ -2668,7 +2669,8 @@ static int create_recorder(struct buffer_instance *instance, int cpu,
 	}
 
 	while (!finished) {
-		if (tracecmd_start_recording(recorder, sleep_time) < 0)
+		if (tracecmd_start_recording(recorder, sleep_time,
+					     initial_sleep_time) < 0)
 			break;
 	}
 	tracecmd_free_recorder(recorder);
@@ -4211,6 +4213,7 @@ enum {
 	OPT_funcstack		= 254,
 	OPT_date		= 255,
 	OPT_module		= 256,
+	OPT_initital_delay	= 257,
 };
 
 void trace_stop(int argc, char **argv)
@@ -4452,6 +4455,7 @@ static void parse_record_options(int argc,
 			{"quiet", no_argument, NULL, OPT_quiet},
 			{"help", no_argument, NULL, '?'},
 			{"module", required_argument, NULL, OPT_module},
+			{"initital-delay", required_argument, NULL, OPT_initital_delay},
 			{NULL, 0, NULL, 0}
 		};
 
@@ -4732,6 +4736,11 @@ static void parse_record_options(int argc,
 			ctx->instance->filter_mod = optarg;
 			ctx->filtered = 0;
 			break;
+		case OPT_initital_delay:
+			if (!optarg)
+				usage(argv);
+			initial_sleep_time = atoi(optarg);
+			break;
 		case OPT_quiet:
 		case 'q':
 			quiet = 1;
diff --git a/trace-recorder.c b/trace-recorder.c
index 85150fd..a48c9e8 100644
--- a/trace-recorder.c
+++ b/trace-recorder.c
@@ -439,7 +439,8 @@ long tracecmd_flush_recording(struct tracecmd_recorder *recorder)
 	return total;
 }
 
-int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long sleep)
+int tracecmd_start_recording(struct tracecmd_recorder *recorder,
+			     unsigned long sleep, unsigned long initital_sleep)
 {
 	struct timespec req;
 	long read = 1;
@@ -447,6 +448,12 @@ int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long s
 
 	recorder->stop = 0;
 
+	if (initital_sleep) {
+		req.tv_sec = initital_sleep / 1000000;
+		req.tv_nsec = (initital_sleep % 1000000) * 1000;
+		nanosleep(&req, NULL);
+	}
+
 	do {
 		/* Only sleep if we did not read anything last time */
 		if (!read && sleep) {
-- 
2.14.3