[PATCH] perf evlist: Fix error out while applying initial delay and LBR

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

Perf record will error out if both --delay and LBR are applied.
For example:
  perf record -D 1000 -a -e cycles -j any -- sleep 2
  Error:
  dummy:HG: PMU Hardware doesn't support sampling/overflow-interrupts.
  Try 'perf stat'

A dummy event is added implicitly for initial delay, which has the same
configurations as real sampling events. The dummy event is a software
event. If LBR is configured, perf must error out.

The dummy event only be used to track PERF_RECORD_MMAP while perf waits
for the initial delay to enable the real events. The BRANCH_STACK bit
can be safely cleared for the dummy event.

After applying the patch:
  perf record -D 1000 -a -e cycles -j any -- sleep 2
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 1.054 MB perf.data (828 samples) ]

Reported-by: Pandey, Sunil K <sunil.k.pandey@xxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
 tools/perf/util/evsel.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 94fce4f..0d55047 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -848,6 +848,12 @@ static void apply_config_terms(struct perf_evsel *evsel,
 	}
 }
 
+static bool is_dummy_event(struct perf_evsel *evsel)
+{
+	return (evsel->attr.type == PERF_TYPE_SOFTWARE) &&
+	       (evsel->attr.config == PERF_COUNT_SW_DUMMY);
+}
+
 /*
  * The enable_on_exec/disabled value strategy:
  *
@@ -1086,6 +1092,14 @@ void perf_evsel__config(struct perf_evsel *evsel, struct record_opts *opts,
 		else
 			perf_evsel__reset_sample_bit(evsel, PERIOD);
 	}
+
+	/*
+	 * For initial_delay, a dummy event is added implicitly.
+	 * The software event will trigger -EOPNOTSUPP error out,
+	 * if BRANCH_STACK bit is set.
+	 */
+	if (opts->initial_delay && is_dummy_event(evsel))
+		perf_evsel__reset_sample_bit(evsel, BRANCH_STACK);
 }
 
 static int perf_evsel__alloc_fd(struct perf_evsel *evsel, int ncpus, int nthreads)
-- 
2.7.4