linux-kernel - Re: [PATCH v2 2/2] perf cs-etm: Add support sample flags

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Date:   Mon, 19 Nov 2018 16:22:02 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.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,
        Mike Leach <mike.leach@...aro.org>,
        Robert Walker <robert.walker@....com>,
        Al Grant <Al.Grant@....com>,
        Coresight ML <coresight@...ts.linaro.org>
Subject: Re: [PATCH v2 2/2] perf cs-etm: Add support sample flags

On Sun, Nov 11, 2018 at 01:07:56PM +0800, Leo Yan wrote:
> We have prepared the flags in the packet structure, so need to copy
> the related value into sample structure thus perf tool can facilitate
> sample flags.
> 
> The PREV_PACKET contains the branch instruction flags and PACKET
> actually contains the flags for next branch instruction.  So this patch
> is to set sample flags with 'etmq->prev_packet->flags'.
> 
> This patch includes three fixing up for sample flags based on the
> packets context:
> 
> - If the packet is exception packet or exception return packet, update
>   the previous packet for exception specific flags;
> - If there has TRACE_ON or TRACE_OFF packet in the middle of instruction
>   packets, this indicates the trace is discontinuous, so append the flag
>   PERF_IP_FLAG_TRACE_END to the previous packet to indicate the trace
>   has been ended;
> - If one instruction packet is behind TRACE_OFF packet, this instruction
>   is restarting trace packet.  So set flag PERF_IP_FLAG_TRACE_START to
>   TRACE_OFF packet if one, this flag isn't used by TRACE_OFF packet but
>   used to indicate trace restarting when generate sample.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/util/cs-etm.c | 43 +++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 455f132..afca6f3 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -676,7 +676,7 @@ static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
>  	sample.stream_id = etmq->etm->instructions_id;
>  	sample.period = period;
>  	sample.cpu = etmq->packet->cpu;
> -	sample.flags = 0;
> +	sample.flags = etmq->prev_packet->flags;
>  	sample.insn_len = 1;
>  	sample.cpumode = event->sample.header.misc;
>  
> @@ -735,7 +735,7 @@ static int cs_etm__synth_branch_sample(struct cs_etm_queue *etmq)
>  	sample.stream_id = etmq->etm->branches_id;
>  	sample.period = 1;
>  	sample.cpu = etmq->packet->cpu;
> -	sample.flags = 0;
> +	sample.flags = etmq->prev_packet->flags;
>  	sample.cpumode = event->sample.header.misc;
>  
>  	/*
> @@ -878,6 +878,43 @@ static int cs_etm__synth_events(struct cs_etm_auxtrace *etm,
>  	return 0;
>  }
>  
> +static void cs_etm__fixup_flags(struct cs_etm_queue *etmq)
> +{
> +	/*
> +	 * Decoding stream might insert one TRACE_OFF packet in the
> +	 * middle of instruction packets, this means it doesn't
> +	 * contain the pair packets with TRACE_OFF and TRACE_ON.
> +	 * For this case, the instruction packet follows with
> +	 * TRACE_OFF packet so we need to fixup prev_packet with flag
> +	 * PERF_IP_FLAG_TRACE_BEGIN, this flag finally is used by the
> +	 * instruction packet to generate samples.
> +	 */
> +	if (etmq->prev_packet->sample_type == CS_ETM_TRACE_OFF &&
> +	    etmq->packet->sample_type == CS_ETM_RANGE)
> +		etmq->prev_packet->flags = PERF_IP_FLAG_BRANCH |
> +					   PERF_IP_FLAG_TRACE_BEGIN;
> +
> +	if (etmq->prev_packet->sample_type == CS_ETM_RANGE) {
> +		/*
> +		 * When the exception packet is inserted, update flags
> +		 * so tell perf it is exception related branches.
> +		 */
> +		if (etmq->packet->sample_type == CS_ETM_EXCEPTION ||
> +		    etmq->packet->sample_type == CS_ETM_EXCEPTION_RET)
> +			etmq->prev_packet->flags = etmq->packet->flags;
> +
> +		/*
> +		 * The trace is discontinuous, weather this is caused by
> +		 * TRACE_ON packet or TRACE_OFF packet is coming, if the
> +		 * previous packet is instruction packet, simply set flag
> +		 * PERF_IP_FLAG_TRACE_END for previous packet.
> +		 */
> +		if (etmq->packet->sample_type == CS_ETM_TRACE_ON ||
> +		    etmq->packet->sample_type == CS_ETM_TRACE_OFF)
> +			etmq->prev_packet->flags |= PERF_IP_FLAG_TRACE_END;
> +	}
> +}
> +

I think it would be better to keep all the flag related processing in
cs-etm-decoder.c so that things in cs-etm.c are only concered with dealing with
perf.

Look at function cs_etm__alloc_queue(), there you'll find "d_params.data = etmq".

In function cs_etm_decoder__new(), decoder->data = d_params->data;

This means that anywhere you have a decoder, decoder->data is an etmq.  I've
used this profusely in my work on CPU-wide trace scenarios.  Because you're
getting there ahead of me you'll need to fix the declaration of struct
cs_etm_queue but that's easy.

Regards,
Mathieu 

>  static int cs_etm__sample(struct cs_etm_queue *etmq)
>  {
>  	struct cs_etm_auxtrace *etm = etmq->etm;
> @@ -1100,6 +1137,8 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
>  					 */
>  					break;
>  
> +				cs_etm__fixup_flags(etmq);
> +
>  				switch (etmq->packet->sample_type) {
>  				case CS_ETM_RANGE:
>  					/*
> -- 
> 2.7.4
>