trace-cmd: Add sleep_time between splice reads

I found that tracing few events causes trace-cmd to almost spin
in a busy loop since it can constantly read a page, and the process
of reading that page causes it to run again. We end up just causing
events to read.

This adds a -s sleep time option that forces trace-cmd to sleep.
The default is 1ms. But it can be disabled with 0.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 16 insertions, 5 deletions

diff --git a/trace-cmd.c b/trace-cmd.c
index 0d53e8c..92008cd 100644
--- a/trace-cmd.c
+++ b/trace-cmd.c
@@ -51,7 +51,7 @@ unsigned int page_size;
 static const char *output_file = "trace.dat";
 
 static int latency;
-
+static int sleep_time = 1000;
 static int cpu_count;
 static int *pids;
 
@@ -568,7 +568,7 @@ static int create_recorder(int cpu)
 
         if (!recorder)
                 die ("can't create recorder");
-        tracecmd_start_recording(recorder);
+        tracecmd_start_recording(recorder, sleep_time);
         tracecmd_free_recorder(recorder);
 
         exit(0);
@@ -631,12 +631,13 @@ void usage(char **argv)
         printf("\n"
                "%s version %s\n\n"
                "usage:\n"
-               " %s record [-e event][-p plugin] [-d] [-o file] [-O option ] [command ...]\n"
+               " %s record [-e event][-p plugin][-d][-o file][-s usecs][-O option ] [command ...]\n"
                "          -e run command with event enabled\n"
                "          -p run command with plugin enabled\n"
                "          -d disable function tracer when running\n"
                "          -o data output file [default trace.dat]\n"
                "          -O option to enable (or disable)\n"
+               "          -s sleep interval between recording (in usecs) [default: 1000]\n"
                "\n"
                " %s start [-e event][-p plugin] [-d] [-O option ]\n"
                "          Uses same options as record, but does not run a command.\n"
@@ -726,6 +727,9 @@ int main (int argc, char **argv)
                                 option = optarg;
                                 set_option(option);
                                 break;
+                        case 's':
+                                sleep_time = atoi(optarg);
+                                break;
                         }
                 }
 
diff --git a/trace-cmd.h b/trace-cmd.h
index 564c959..27f30a7 100644
--- a/trace-cmd.h
+++ b/trace-cmd.h
@@ -107,7 +107,7 @@ void tracecmd_output_close(struct tracecmd_output *handle);
 
 void tracecmd_free_recorder(struct tracecmd_recorder *recorder);
 struct tracecmd_recorder *tracecmd_create_recorder(const char *file, int cpu);
-int tracecmd_start_recording(struct tracecmd_recorder *recorder);
+int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long sleep);
 void tracecmd_stop_recording(struct tracecmd_recorder *recorder);
 
 
diff --git a/trace-record.c b/trace-record.c
index 0cd81ac..96579f1 100644
--- a/trace-record.c
+++ b/trace-record.c
@@ -92,14 +92,21 @@ struct tracecmd_recorder *tracecmd_create_recorder(const char *file, int cpu)
         return NULL;
 }
 
-int tracecmd_start_recording(struct tracecmd_recorder *recorder)
+int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long sleep)
 {
+        struct timespec req;
         char *buf[recorder->page_size];
         int ret;
 
         recorder->stop = 0;
 
         do {
+                if (sleep) {
+                        req.tv_sec = sleep / 1000000;
+                        req.tv_nsec = (sleep % 1000000) * 1000;
+                        nanosleep(&req, NULL);
+                }
+
                 ret = splice(recorder->trace_fd, NULL, recorder->brass[1], NULL,
                              recorder->page_size, 1 /* SPLICE_F_MOVE */);
                 if (ret < 0) {