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Subject[PATCH] perf evlist: Fix error out while applying initial delay and LBR
Date
From: Kan Liang <kan.liang@linux.intel.com>

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@intel.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
---
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
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