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

From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Leo Yan <leo.yan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Coresight ML <coresight@lists.linaro.org>,
	linux-kernel@vger.kernel.org, Namhyung Kim <namhyung@kernel.org>,
	Robert Walker <robert.walker@arm.com>,
	Jiri Olsa <jolsa@redhat.com>,
	linux-arm-kernel@lists.infradead.org,
	Mike Leach <mike.leach@linaro.org>
Subject: Re: [PATCH v3 6/8] perf cs-etm: Treat NO_SYNC element as trace discontinuity
Date: Thu, 13 Dec 2018 09:38:54 -0300	[thread overview]
Message-ID: <20181213123854.GE21027@kernel.org> (raw)
In-Reply-To: <1544513908-16805-7-git-send-email-leo.yan@linaro.org>

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.
> 
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Robert Walker <robert.walker@arm.com>
> ---
>  tools/perf/util/cs-etm-decoder/cs-etm-decoder.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> 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 1039f364..bee026e 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);
> -- 
> 2.7.4

-- 

- Arnaldo

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