Re: [PATCH v3 6/8] perf cs-etm: Treat NO_SYNC element as trace discontinuity

leo.yan
2018-12-13T13:10:12Z

Hi Arnaldo,

On Thu, Dec 13, 2018 at 09:41:54AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Dec 13, 2018 at 09:38:54AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Tue, Dec 11, 2018 at 03:38:26PM +0800, Leo Yan escreveu:
> > > CoreSight tracer driver might insert barrier packet between different
> > > buffers, thus the decoder can spot the boundaries based on the barrier
> > > packet; the decoder is possible to hit a barrier packet and emit a
> > > NO_SYNC element, then the decoder will find a periodic synchronisation
> > > point inside that next trace block that starts trace again but does not
> > > have the TRACE_ON element as indicator - usually because this block of
> > > trace has wrapped the buffer so we have lost the original point that
> > > trace was enabled.
> > >
> > > In upper case, it results in the trace stream only inserts the
> > > OCSD_GEN_TRC_ELEM_NO_SYNC element in the middle of tracing stream, but
> > > we don't handle NO_SYNC element properly and at the end users miss to
> > > see the info for trace discontinuity.
> >
> >
> > "In upper case"? Maybe:
> >
> > In the former case it causes the insertion of a OCSD_GEN_TRC_ELEM_NO_SYNC
> > in the middle of the the tracing stream, but as we were npt handling the
> > NO_SYNC element properly which ends up making users miss the
> > discontinuity indication"?
>
> > > Though OCSD_GEN_TRC_ELEM_NO_SYNC is different from CS_ETM_TRACE_ON when
> > > output from the decoder, but both of them indicate the trace data is
> >
> > can we remove the "but" and "of them" (redundant) above?
> >
> > > discontinuous; this patch treats OCSD_GEN_TRC_ELEM_NO_SYNC as trace
> > a
> > > discontinuity and generates CS_ETM_DISCONTINUITY packet for it, so
> > > cs-etm can handle discontinuity for this case, finally it saves the last
> > it (way too many "discontinuity")
> > > trace data for previous trace block and restart samples for new block.
>
> I've tentatively done those changes (and a few more) in my local branch,
> resulting in the wording below, plese let me know if you are ok with it:

Very appreciate your helping. Please see some minor typos in below
commit:

> commit 148068b45fe2e93b19c06cfc1140ea12ca72eb59
> Author: Leo Yan <leo.yan@linaro.org>
> Date: Tue Dec 11 15:38:26 2018 +0800
>
> perf cs-etm: Treat NO_SYNC element as trace discontinuity
>
> The CoreSight tracer driver might insert a barrier packets between
packet
> different buffers, thus the decoder can spot the boundaries based on the
> barrier packet; it is possible for the decoder to hit a barrier packet
> and emit a NO_SYNC element, then the decoder will find a periodic
> synchronisation point inside that next trace block that starts the trace
> again but does not have the TRACE_ON element as indicator - usually
> because this trace block has wrapped the buffer so we have lost the
> original point when the trace was enabled.
>
> In the first case it causes the insertion of a OCSD_GEN_TRC_ELEM_NO_SYNC
former
> in the middle of the the tracing stream, but as we were npt handling the
not
> NO_SYNC element properly which ends up making users miss the
> discontinuity indication"?
s/?/.

Thanks a lot for helping. If you prefer me to resend the patch set,
also let me know.

> Though OCSD_GEN_TRC_ELEM_NO_SYNC is different from CS_ETM_TRACE_ON when
> output from the decoder, both indicate that the trace data is
> discontinuous; this patch treats OCSD_GEN_TRC_ELEM_NO_SYNC as a trace
> discontinuity and generates a CS_ETM_DISCONTINUITY packet for it, so
> cs-etm can handle the discontinuity for this case, finally it saves the
> last trace data for the previous trace block and restart samples for the
> new block.
>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Robert Walker <robert.walker@arm.com>
> Cc: coresight ml <coresight@lists.linaro.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Link: http://lkml.kernel.org/r/1544513908-16805-7-git-send-email-leo.yan@linaro.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>
> diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> index 1039f364f4cc..bee026e76a4c 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> @@ -410,7 +410,6 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
> case OCSD_GEN_TRC_ELEM_UNKNOWN:
> break;
> case OCSD_GEN_TRC_ELEM_NO_SYNC:
> - break;
> case OCSD_GEN_TRC_ELEM_TRACE_ON:
> resp = cs_etm_decoder__buffer_discontinuity(decoder,
> trace_chan_id);
>
>