perf record: Do not ask for precise_ip with --no-samples

Commit-ID:  4b4cd50319127b3b606b8aaf3426d8972df1666a
Gitweb:     http://git.kernel.org/tip/4b4cd50319127b3b606b8aaf3426d8972df1666a
Author:     Arnaldo Carvalho de Melo <[email protected]>
AuthorDate: Mon, 3 Jul 2017 13:26:32 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Tue, 18 Jul 2017 23:14:13 -0300

perf record: Do not ask for precise_ip with --no-samples

When the user doesn't specify an event with -e/--event, 'perf record' will use as a default the "cycles" event with the highest level of precision in perf_event_attr.precise_ip, but --no-samples, if present, is incompatible with precise_ip != 0, so use the newly introduced __perf_event__add_default(precise = false) to fix that:

Before:

  # perf record -n usleep 1
  Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
  Error:
  The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cycles:ppp).
  /bin/dmesg may provide additional information.
  No CONFIG_PERF_EVENTS=y kernel support configured?
  #

After:

  # perf record -n usleep 1
  Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.018 MB perf.data ]
  [root@jouet /]# perf evlist -v
  cycles: size: 112, sample_type: IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1
  [root@jouet /]#

---
 tools/perf/builtin-record.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 17a14bc..64eef9a5 100644
@@ -1821,7 +1821,7 @@ int cmd_record(int argc, const char **argv)
 		record.opts.tail_synthesize = true;
 
 	if (rec->evlist->nr_entries == 0 &&
-	    perf_evlist__add_default(rec->evlist) < 0) {
+	    __perf_evlist__add_default(rec->evlist, !record.opts.no_samples) < 0) {
 		pr_err("Not enough memory for event selector list\n");
 		goto out;
 	}