Re: [PATCH v7 2/2] perf cs-etm: Split --dump-raw-trace by AUX records

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

On Mon, Jun 28, 2021 at 11:38:34AM +0100, James Clark wrote:

[...]

> >>  static int cs_etm__process_auxtrace_event(struct perf_session *session,
> >>  					  union perf_event *event,
> >>  					  struct perf_tool *tool __maybe_unused)
> >> @@ -2462,7 +2478,8 @@ static int cs_etm__process_auxtrace_event(struct perf_session *session,
> >>  				cs_etm__dump_event(etm, buffer);
> >>  				auxtrace_buffer__put_data(buffer);
> >>  			}
> >> -	}
> >> +	} else if (dump_trace)
> >> +		dump_queued_data(etm, &event->auxtrace);
> > 
> > IIUC, in the function cs_etm__process_auxtrace_event(), since
> > "etm->data_queued" is always true, below flow will never run:
> > 
> >     if (!etm->data_queued) {
> >         ......
> > 
> >         if (dump_trace)
> >             if (auxtrace_buffer__get_data(buffer, fd)) {
> >                     cs_etm__dump_event(etm, buffer);
> >                     auxtrace_buffer__put_data(buffer);
> >             }
> >     }
> > 
> > If so, it's better to use a new patch to polish the code.
> > 
> 
> Hi Leo,
> 
> I think this is not true in piped mode because there is no auxtrace index.
> In that mode, events are processed only in file order and cs_etm__process_auxtrace_event()
> is called for each buffer.
> 
> You can reproduce this with something like this:
> 
>      ./perf record -o - ls > stdio.data
>      cat stdio.data | ./perf report -i -

You are right!  I tried these two commands with cs_etm event, just as
you said, in this case, the AUX trace data is not queued; so the flow
for "if (!etm->data_queued)" should be kept.  If so, I am very fine
for current change.  Thanks for sharing the knowledge.

> There are some other Coresight features that don't work as expected in this mode, like
> sorting timestamps between CPUs. The aux split patchset won't work either because random
> access isn't possible. And the TRBE patch that I'm working on now won't work, because it
> also requires the random access to lookup the flags on the AUX record to configure the 
> decoder for unformatted trace.

Cool, looking forward for the patches :)

Leo