perf trace: Improve event processing exit

We need to differentiate SIGCHLD from SIGINT, the later should cause as
immediate as possible exit, while the former should wait to process the
events that may be perceived in the ring buffer after the SIGCHLD is
handled.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-vf6n57ewm3mjy2sz6r491hus@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -1098,10 +1098,12 @@ static size_t trace__fprintf_tstamp(struct trace *trace, u64 tstamp, FILE *fp)
 }
 
 static bool done = false;
+static bool interrupted = false;
 
-static void sig_handler(int sig __maybe_unused)
+static void sig_handler(int sig)
 {
 	done = true;
+	interrupted = sig == SIGINT;
 }
 
 static size_t trace__fprintf_entry_head(struct trace *trace, struct thread *thread,
@@ -1771,24 +1773,23 @@ again:
 			handler = evsel->handler.func;
 			handler(trace, evsel, &sample);
 
-			if (done)
-				goto out_unmap_evlist;
+			if (interrupted)
+				goto out_disable;
 		}
 	}
 
 	if (trace->nr_events == before) {
-		if (done)
-			goto out_unmap_evlist;
+		int timeout = done ? 100 : -1;
 
-		poll(evlist->pollfd, evlist->nr_fds, -1);
+		if (poll(evlist->pollfd, evlist->nr_fds, timeout) > 0)
+			goto again;
+	} else {
+		goto again;
 	}
 
-	if (done)
-		perf_evlist__disable(evlist);
-	else
-		goto again;
+out_disable:
+	perf_evlist__disable(evlist);
 
-out_unmap_evlist:
 	if (!err) {
 		if (trace->summary)
 			trace__fprintf_thread_summary(trace, trace->output);