linux-kernel - Re: [PATCH v3 6/8] perf cs-etm: Treat NO

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Date:   Thu, 13 Dec 2018 21:23:40 +0800
From:   leo.yan@...aro.org
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Coresight ML <coresight@...ts.linaro.org>,
        Mike Leach <mike.leach@...aro.org>,
        Robert Walker <robert.walker@....com>
Subject: Re: [PATCH v3 6/8] perf cs-etm: Treat NO_SYNC element as trace
 discontinuity

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

[...]

> > > commit 148068b45fe2e93b19c06cfc1140ea12ca72eb59
> > > Author: Leo Yan <leo.yan@...aro.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@...aro.org>
> > >     Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > >     Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > >     Cc: Jiri Olsa <jolsa@...hat.com>
> > >     Cc: Mike Leach <mike.leach@...aro.org>
> > >     Cc: Namhyung Kim <namhyung@...nel.org>
> > >     Cc: Robert Walker <robert.walker@....com>
> > >     Cc: coresight ml <coresight@...ts.linaro.org>
> > >     Cc: linux-arm-kernel@...ts.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@...hat.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