[PATCH v1 2/2] arm64: perf: Report error if PMU fails to support current CPU

[Leo Yan <leo.yan@linaro.org>]

When run perf command on the Arm big.LITTLE system (Juno-r2 board):

  perf record -e cycles --per-thread program

The command executes normally without any errors; but when report the
result with "perf report", it fails to parse the symbols.  This is
because the perf data file doesn't contain MMAP2 events, thus it cannot
find the correct object file for parsing symbols.

On the big.LITTLE system, if the initialized PMU doesn't match with the
CPU the profiled task is scheduled on; for example, the initialized PMU
is on CPU0 in the LITTLE cluster, when invoke the function
perf_event_mmap_event() on CPU2 in the big cluster, the event is always
filtered out due to the CPU2 is not supported by the initialized PMU.
Finally, there have no any MMAP2 samples are generated for the
profiling.

This patch doesn't fix for this issue, alternatively, it simply reports
an error when detect the current CPU is not supported by PMU, so can
remind the user for the abnormal situation.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 drivers/perf/arm_pmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index aedea060ca8b..99ddc8bf6466 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -565,6 +565,9 @@ static int armpmu_filter_match(struct perf_event *event)
 	int ret;
 
 	ret = cpumask_test_cpu(cpu, &armpmu->supported_cpus);
+	if (!ret)
+		pr_err("PMU doesn't support current CPU %d\n", cpu);
+
 	if (ret && armpmu->filter_match)
 		return armpmu->filter_match(event);
 
-- 
2.25.1