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Date:   Tue, 13 Feb 2018 15:22:33 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Robert Walker <robert.walker@....com>
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org
Subject: Re: [PATCH 2/2] perf inject: Emit instruction records on ETM trace
 discontinuity

On Wed, Feb 07, 2018 at 01:57:25PM +0000, Robert Walker wrote:
> There may be discontinuities in the ETM trace stream due to overflows or
> ETM configuration for selective trace.  This patch emits an instruction
> sample with the pending branch stack when a TRACE ON packet occurs
> indicating a discontinuity in the trace data.
> 
> A new packet type CS_ETM_TRACE_ON is added, which is emitted by the low
> level decoder when a TRACE ON occurs.  The higher level decoder flushes the
> branch stack when this packet is emitted.
> 
> Signed-off-by: Robert Walker <robert.walker@....com>
> ---
>  tools/perf/util/cs-etm-decoder/cs-etm-decoder.c |  9 +++
>  tools/perf/util/cs-etm-decoder/cs-etm-decoder.h |  1 +
>  tools/perf/util/cs-etm.c                        | 84 +++++++++++++++++--------
>  3 files changed, 69 insertions(+), 25 deletions(-)
> 
> 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 8ff69df..640af88 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> @@ -328,7 +328,14 @@ cs_etm_decoder__buffer_range(struct cs_etm_decoder *decoder,
>  	}
>  
>  	return ret;
> +}
>  
> +static ocsd_datapath_resp_t
> +cs_etm_decoder__buffer_trace_on(struct cs_etm_decoder *decoder,
> +				const uint8_t trace_chan_id)
> +{
> +	return cs_etm_decoder__buffer_packet(decoder, trace_chan_id,
> +					     CS_ETM_TRACE_ON);
>  }
>  
>  static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
> @@ -347,6 +354,8 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
>  		decoder->trace_on = false;
>  		break;
>  	case OCSD_GEN_TRC_ELEM_TRACE_ON:
> +		resp = cs_etm_decoder__buffer_trace_on(decoder,
> +						       trace_chan_id);
>  		decoder->trace_on = true;
>  		break;
>  	case OCSD_GEN_TRC_ELEM_INSTR_RANGE:
> diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> index a4fdd28..743f5f4 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> @@ -24,6 +24,7 @@ struct cs_etm_buffer {
>  
>  enum cs_etm_sample_type {
>  	CS_ETM_RANGE = 1 << 0,
> +	CS_ETM_TRACE_ON = 1 << 1,
>  };
>  
>  struct cs_etm_packet {
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 6777246..a8d07bd 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -866,6 +866,8 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
>  	 * PREV_PACKET is a branch.
>  	 */
>  	if (etm->synth_opts.last_branch &&
> +	    etmq->prev_packet &&
> +	    etmq->prev_packet->sample_type == CS_ETM_RANGE &&
>  	    etmq->prev_packet->last_instr_taken_branch)
>  		cs_etm__update_last_branch_rb(etmq);
>  
> @@ -918,6 +920,40 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
>  	return 0;
>  }
>  
> +static int cs_etm__flush(struct cs_etm_queue *etmq)
> +{
> +	int err = 0;
> +	struct cs_etm_packet *tmp;
> +
> +	if (etmq->etm->synth_opts.last_branch &&
> +	    etmq->prev_packet &&
> +	    etmq->prev_packet->sample_type == CS_ETM_RANGE) {
> +		/*
> +		 * Generate a last branch event for the branches left in the
> +		 * circular buffer at the end of the trace.
> +		 *
> +		 * Use the address of the end of the last reported execution
> +		 * range
> +		 */
> +		u64 addr = cs_etm__last_executed_instr(etmq->prev_packet);
> +
> +		err = cs_etm__synth_instruction_sample(
> +			etmq, addr,
> +			etmq->period_instructions);
> +		etmq->period_instructions = 0;
> +
> +		/*
> +		 * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for
> +		 * the next incoming packet.
> +		 */
> +		tmp = etmq->packet;
> +		etmq->packet = etmq->prev_packet;
> +		etmq->prev_packet = tmp;
> +	}
> +
> +	return err;
> +}
> +
>  static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
>  {
>  	struct cs_etm_auxtrace *etm = etmq->etm;
> @@ -946,20 +982,19 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
>  		/* Run trace decoder until buffer consumed or end of trace */
>  		do {
>  			processed = 0;
> -

this...

>  			err = cs_etm_decoder__process_data_block(
>  				etmq->decoder,
>  				etmq->offset,
>  				&buffer.buf[buffer_used],
>  				buffer.len - buffer_used,
>  				&processed);
> -

and this should have gone in the first patch.

>  			if (err)
>  				return err;
>  
>  			etmq->offset += processed;
>  			buffer_used += processed;
>  
> +			/* Process each packet in this chunk */

And probably this too.

With the above changes:

Acked-by: Mathieu Poirier <mathieu.poirier@...aro.org>

>  			while (1) {
>  				err = cs_etm_decoder__get_packet(etmq->decoder,
>  								 etmq->packet);
> @@ -970,32 +1005,31 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
>  					 */
>  					break;
>  
> -				/*
> -				 * If the packet contains an instruction
> -				 * range, generate instruction sequence
> -				 * events.
> -				 */
> -				if (etmq->packet->sample_type & CS_ETM_RANGE)
> -					err = cs_etm__sample(etmq);
> +				switch (etmq->packet->sample_type) {
> +				case CS_ETM_RANGE:
> +					/*
> +					 * If the packet contains an instruction
> +					 * range, generate instruction sequence
> +					 * events.
> +					 */
> +					cs_etm__sample(etmq);
> +					break;
> +				case CS_ETM_TRACE_ON:
> +					/*
> +					 * Discontinuity in trace, flush
> +					 * previous branch stack
> +					 */
> +					cs_etm__flush(etmq);
> +					break;
> +				default:
> +					break;
> +				}
>  			}
>  		} while (buffer.len > buffer_used);
>  
> -		/*
> -		 * Generate a last branch event for the branches left in
> -		 * the circular buffer at the end of the trace.
> -		 */
> -		if (etm->sample_instructions &&
> -		    etmq->etm->synth_opts.last_branch) {
> -			struct branch_stack *bs = etmq->last_branch_rb;
> -			struct branch_entry *be =
> -				&bs->entries[etmq->last_branch_pos];
> -
> -			err = cs_etm__synth_instruction_sample(
> -				etmq, be->to, etmq->period_instructions);
> -			if (err)
> -				return err;
> -		}
> -
> +		if (err == 0)
> +			/* Flush any remaining branch stack entries */
> +			err = cs_etm__flush(etmq);
>  	}
>  
>  	return err;
> -- 
> 2.7.4
> 

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