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

leo.yan
2018-12-13T13:23:53Z

On Thu, Dec 13, 2018 at 10:21:26AM -0300, Arnaldo Carvalho de Melo wrote:

[...]

> > > 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
>
> I'll remove the 'a' instead, ok?

Yeah.

> > > 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.
>
> I can fix it, here.

Thanks a lot!

> > > 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);
> > >
> > >
>
> --
>
> - Arnaldo