Messages in this thread |  | | Subject | Re: [RFC 09/11] coresight: etm-perf: Disable the path before capturing the trace data | From | Suzuki K Poulose <> | Date | Mon, 23 Nov 2020 10:01:32 +0000 |
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On 11/23/20 6:08 AM, Anshuman Khandual wrote: > > > 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.
Yes, once we update the buffer from within the sink_ops->disable(), we don't need the update buffer anymore. It is pointless to have a function that is provided to the external user.
> >> >> 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 ? >
In sysfs mode, we already do an action similar to "update buffer" for all the sinks. (e.g, see tmc_etr_sync_sysfs_buf() ). i.e, update the buffer before the sink is disabled. That is the same we propose above.
Suzuki
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