perf record: Properly synchronize child creation

Remove that ugly usleep and provide proper serialization between
parent and child just like perf-stat does.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: fweisbec@gmail.com
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091216165904.908184135@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 65301c5ca1dedcffcc473c35767b01960cba19dd..9b7c6d887d5a9ad4cfca9cffc024218204385b57 100644 (file)
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -402,7 +402,7 @@ static void atexit_header(void)
        perf_header__write(&session->header, output, true);
 }
 
-static int __cmd_record(int argc, const char **argv)
+static int __cmd_record(int argc __used, const char **argv)
 {
        int i, counter;
        struct stat st;
@@ -410,6 +410,8 @@ static int __cmd_record(int argc, const char **argv)
        int flags;
        int err;
        unsigned long waking = 0;
+       int child_ready_pipe[2], go_pipe[2];
+       char buf;
 
        page_size = sysconf(_SC_PAGE_SIZE);
        nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
@@ -420,6 +422,11 @@ static int __cmd_record(int argc, const char **argv)
        signal(SIGCHLD, sig_handler);
        signal(SIGINT, sig_handler);
 
+       if (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0) {
+               perror("failed to create pipes");
+               exit(-1);
+       }
+
        if (!stat(output_name, &st) && st.st_size) {
                if (!force) {
                        if (!append_file) {
@@ -476,19 +483,65 @@ static int __cmd_record(int argc, const char **argv)
 
        atexit(atexit_header);
 
-       if (!system_wide) {
-               pid = target_pid;
-               if (pid == -1)
-                       pid = getpid();
+       if (target_pid == -1) {
+               pid = fork();
+               if (pid < 0) {
+                       perror("failed to fork");
+                       exit(-1);
+               }
 
-               open_counters(profile_cpu, pid);
-       } else {
-               if (profile_cpu != -1) {
-                       open_counters(profile_cpu, target_pid);
-               } else {
-                       for (i = 0; i < nr_cpus; i++)
-                               open_counters(i, target_pid);
+               if (!pid) {
+                       close(child_ready_pipe[0]);
+                       close(go_pipe[1]);
+                       fcntl(go_pipe[0], F_SETFD, FD_CLOEXEC);
+
+                       /*
+                        * Do a dummy execvp to get the PLT entry resolved,
+                        * so we avoid the resolver overhead on the real
+                        * execvp call.
+                        */
+                       execvp("", (char **)argv);
+
+                       /*
+                        * Tell the parent we're ready to go
+                        */
+                       close(child_ready_pipe[1]);
+
+                       /*
+                        * Wait until the parent tells us to go.
+                        */
+                       if (read(go_pipe[0], &buf, 1) == -1)
+                               perror("unable to read pipe");
+
+                       execvp(argv[0], (char **)argv);
+
+                       perror(argv[0]);
+                       exit(-1);
                }
+
+               child_pid = pid;
+
+               if (!system_wide)
+                       target_pid = pid;
+
+               close(child_ready_pipe[1]);
+               close(go_pipe[0]);
+               /*
+                * wait for child to settle
+                */
+               if (read(child_ready_pipe[0], &buf, 1) == -1) {
+                       perror("unable to read pipe");
+                       exit(-1);
+               }
+               close(child_ready_pipe[0]);
+       }
+
+
+       if (!system_wide || profile_cpu != -1) {
+               open_counters(profile_cpu, target_pid);
+       } else {
+               for (i = 0; i < nr_cpus; i++)
+                       open_counters(i, target_pid);
        }
 
        if (file_new) {
@@ -503,31 +556,6 @@ static int __cmd_record(int argc, const char **argv)
        else
                event__synthesize_threads(process_synthesized_event, session);
 
-       if (target_pid == -1 && argc) {
-               pid = fork();
-               if (pid < 0)
-                       die("failed to fork");
-
-               if (!pid) {
-                       if (execvp(argv[0], (char **)argv)) {
-                               perror(argv[0]);
-                               exit(-1);
-                       }
-               } else {
-                       /*
-                        * Wait a bit for the execv'ed child to appear
-                        * and be updated in /proc
-                        * FIXME: Do you know a less heuristical solution?
-                        */
-                       usleep(1000);
-                       event__synthesize_thread(pid,
-                                                process_synthesized_event,
-                                                session);
-               }
-
-               child_pid = pid;
-       }
-
        if (realtime_prio) {
                struct sched_param param;
 
@@ -538,6 +566,11 @@ static int __cmd_record(int argc, const char **argv)
                }
        }
 
+       /*
+        * Let the child rip
+        */
+       close(go_pipe[1]);
+
        for (;;) {
                int hits = samples;
 
@@ -634,7 +667,7 @@ int cmd_record(int argc, const char **argv, const char *prefix __used)
 
        argc = parse_options(argc, argv, options, record_usage,
                            PARSE_OPT_STOP_AT_NON_OPTION);
-       if (!argc && target_pid == -1 && !system_wide)
+       if (!argc && target_pid == -1 && (!system_wide || profile_cpu == -1))
                usage_with_options(record_usage, options);
 
        symbol__init();