Messages in this thread |  | | Subject | Re: [RFC 09/11] coresight: etm-perf: Disable the path before capturing the trace data | From | Anshuman Khandual <> | Date | Mon, 23 Nov 2020 11:38:53 +0530 |
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On 11/12/20 2:57 PM, Suzuki K Poulose wrote: > On 11/10/20 12:45 PM, Anshuman Khandual wrote: >> perf handle structure needs to be shared with the TRBE IRQ handler for >> capturing trace data and restarting the handle. There is a probability >> of an undefined reference based crash when etm event is being stopped >> while a TRBE IRQ also getting processed. This happens due the release >> of perf handle via perf_aux_output_end(). This stops the sinks via the >> link before releasing the handle, which will ensure that a simultaneous >> TRBE IRQ could not happen. >> >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- >> This might cause problem with traditional sink devices which can be >> operated in both sysfs and perf mode. This needs to be addressed >> correctly. One option would be to move the update_buffer callback >> into the respective sink devices. e.g, disable(). >> >> drivers/hwtracing/coresight/coresight-etm-perf.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c >> index 534e205..1a37991 100644 >> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c >> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c >> @@ -429,7 +429,9 @@ static void etm_event_stop(struct perf_event *event, int mode) >> size = sink_ops(sink)->update_buffer(sink, handle, >> event_data->snk_config); >> + coresight_disable_path(path); >> perf_aux_output_end(handle, size); >> + return; >> } > > As you mentioned, this is not ideal where another session could be triggered on > the sink from a different ETM (not for per-CPU sink) in a different mode before > you collect the buffer. I believe the best option is to leave the > update_buffer() to disable_hw. This would need to pass on the "handle" to the > disable_path.
Passing 'handle' into coresight_ops_sink->disable() would enable pushing updated trace data into perf aux buffer. But do you propose to drop the update_buffer() call back completely or just move it into disable() call back (along with PERF_EF_UPDATE mode check) for all individual sinks for now. May be, later it can be dropped off completely.
> > That way the races can be handled inside the sinks. Also, this aligns the > perf mode of the sinks with that of the sysfs mode.
Did not get that, could you please elaborate ?
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