perf record: Create events initially disabled and enable after init

perf-record currently creates events enabled. When doing a system wide
collection (-a arg) this causes data collection for perf's
initialization activities -- eg., perf_event__synthesize_threads().

For some events (e.g., context switch S/W event or tracepoints like
syscalls) perf's initialization causes a lot of events to be captured
frequently generating "Check IO/CPU overload!" warnings on larger
systems (e.g., 2 socket, quad core, hyperthreading).

perf's initialization phase can be skipped by creating events
disabled and then enabling them once the initialization is done.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1314289075-14706-1-git-send-email-dsahern@gmail.comSigned-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -161,6 +161,7 @@ static void config_attr(struct perf_evsel *evsel, struct perf_evlist *evlist)
 	struct perf_event_attr *attr = &evsel->attr;
 	int track = !evsel->idx; /* only the first counter needs these */
 
+	attr->disabled		= 1;
 	attr->inherit		= !no_inherit;
 	attr->read_format	= PERF_FORMAT_TOTAL_TIME_ENABLED |
 				  PERF_FORMAT_TOTAL_TIME_RUNNING |
@@ -671,6 +672,8 @@ static int __cmd_record(int argc, const char **argv)
 		}
 	}
 
+	perf_evlist__enable(evsel_list);
+
 	/*
 	 * Let the child rip
 	 */

tools/perf/util/evlist.c

@@ -113,6 +113,19 @@ void perf_evlist__disable(struct perf_evlist *evlist)
 	}
 }
 
+void perf_evlist__enable(struct perf_evlist *evlist)
+{
+	int cpu, thread;
+	struct perf_evsel *pos;
+
+	for (cpu = 0; cpu < evlist->cpus->nr; cpu++) {
+		list_for_each_entry(pos, &evlist->entries, node) {
+			for (thread = 0; thread < evlist->threads->nr; thread++)
+				ioctl(FD(pos, cpu, thread), PERF_EVENT_IOC_ENABLE);
+		}
+	}
+}
+
 int perf_evlist__alloc_pollfd(struct perf_evlist *evlist)
 {
 	int nfds = evlist->cpus->nr * evlist->threads->nr * evlist->nr_entries;

tools/perf/util/evlist.h

@@ -54,6 +54,7 @@ int perf_evlist__mmap(struct perf_evlist *evlist, int pages, bool overwrite);
 void perf_evlist__munmap(struct perf_evlist *evlist);
 
 void perf_evlist__disable(struct perf_evlist *evlist);
+void perf_evlist__enable(struct perf_evlist *evlist);
 
 static inline void perf_evlist__set_maps(struct perf_evlist *evlist,
 					 struct cpu_map *cpus,