perf evsel: Add 'immediate' option

Add an option to cause a selected event to be enabled immediately when
configured by perf_evsel__config().

This is needed when using the sched_switch tracepoint to follow object
code execution.  By having sched_switch enabled immediately the first
sched_switch event precedes the start of other tracing.
Signed-off-by: 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: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1405332185-4050-34-git-send-email-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -681,6 +681,11 @@ void perf_evsel__config(struct perf_evsel *evsel, struct record_opts *opts)
 	if (target__none(&opts->target) && perf_evsel__is_group_leader(evsel) &&
 		!opts->initial_delay)
 		attr->enable_on_exec = 1;
+
+	if (evsel->immediate) {
+		attr->disabled = 0;
+		attr->enable_on_exec = 0;
+	}
 }
 
 int perf_evsel__alloc_fd(struct perf_evsel *evsel, int ncpus, int nthreads)

tools/perf/util/evsel.h

@@ -84,6 +84,7 @@ struct perf_evsel {
 	bool 			supported;
 	bool 			needs_swap;
 	bool			no_aux_samples;
+	bool			immediate;
 	/* parse modifier helper */
 	int			exclude_GH;
 	int			nr_members;