Subject: Re: [PATCH v2 16/17] perf tools: Add notion of time to decoding code

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Thu, 6 Jun 2019 15:50:27 -0300

Em Fri, May 24, 2019 at 11:35:07AM -0600, Mathieu Poirier escreveu:
> This patch deals with timestamp packets received from the decoding library
> in order to give the front end packet processing loop a handle on the time
> instruction conveyed by range packets have been executed at.
> 
> Signed-off-by: Mathieu Poirier <[email-masked]>
> ---
>  .../perf/util/cs-etm-decoder/cs-etm-decoder.c | 112 +++++++++++++++++-
>  tools/perf/util/cs-etm.c                      |  19 +++
>  tools/perf/util/cs-etm.h                      |  17 +++
>  3 files changed, 144 insertions(+), 4 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 ce85e52f989c..33e975c8d11b 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> @@ -269,6 +269,76 @@ cs_etm_decoder__create_etm_packet_printer(struct cs_etm_trace_params *t_params,
>  						     trace_config);
>  }
>  
> +static ocsd_datapath_resp_t
> +cs_etm_decoder__do_soft_timestamp(struct cs_etm_queue *etmq,
> +				  struct cs_etm_packet_queue *packet_queue,
> +				  const uint8_t trace_chan_id)
> +{
> +	/* No timestamp packet has been received, nothing to do */
> +	if (!packet_queue->timestamp)
> +		return OCSD_RESP_CONT;
> +
> +	packet_queue->timestamp = packet_queue->next_timestamp;
> +
> +	/* Estimate the timestamp for the next range packet */
> +	packet_queue->next_timestamp += packet_queue->instr_count;
> +	packet_queue->instr_count = 0;
> +
> +	/* Tell the front end which traceid_queue needs attention */
> +	cs_etm__etmq_set_traceid_queue_timestamp(etmq, trace_chan_id);
> +
> +	return OCSD_RESP_WAIT;
> +}
> +
> +static ocsd_datapath_resp_t
> +cs_etm_decoder__do_hard_timestamp(struct cs_etm_queue *etmq,
> +				  const ocsd_generic_trace_elem *elem,
> +				  const uint8_t trace_chan_id)
> +{
> +	struct cs_etm_packet_queue *packet_queue;
> +
> +	/* First get the packet queue for this traceID */
> +	packet_queue = cs_etm__etmq_get_packet_queue(etmq, trace_chan_id);
> +	if (!packet_queue)
> +		return OCSD_RESP_FATAL_SYS_ERR;
> +
> +	/*
> +	 * We've seen a timestamp packet before - simply record the new value.
> +	 * Function do_soft_timestamp() will report the value to the front end,
> +	 * hence asking the decoder to keep decoding rather than stopping.
> +	 */
> +	if (packet_queue->timestamp) {
> +		packet_queue->next_timestamp = elem->timestamp;
> +		return OCSD_RESP_CONT;
> +	}
> +
> +	/*
> +	 * This is the first timestamp we've seen since the beginning of traces
> +	 * or a discontinuity.  Since timestamps packets are generated *after*
> +	 * range packets have been generated, we need to estimate the time at
> +	 * which instructions started by substracting the number of instructions
> +	 * executed to the timestamp.
> +	 */
> +	packet_queue->timestamp = elem->timestamp -
> +						packet_queue->instr_count;

No need to break lines like that, in this case it even wouldn't pass the
width used for the comments right above it :-)

I'm fixing it up this time.

Something else, all the patches in this series, so far, needed to have
as the subject prefix "perf cs-etm: ...", not the generic one "perf
tools: ...". I'm fixing it up as well, no need to resend.

- Arnaldo

> +	packet_queue->next_timestamp = elem->timestamp;
> +	packet_queue->instr_count = 0;
> +
> +	/* Tell the front end which traceid_queue needs attention */
> +	cs_etm__etmq_set_traceid_queue_timestamp(etmq, trace_chan_id);
> +
> +	/* Halt processing until we are being told to proceed */
> +	return OCSD_RESP_WAIT;
> +}
> +
> +static void
> +cs_etm_decoder__reset_timestamp(struct cs_etm_packet_queue *packet_queue)
> +{
> +	packet_queue->timestamp = 0;
> +	packet_queue->next_timestamp = 0;
> +	packet_queue->instr_count = 0;
> +}
> +
>  static ocsd_datapath_resp_t
>  cs_etm_decoder__buffer_packet(struct cs_etm_packet_queue *packet_queue,
>  			      const u8 trace_chan_id,
> @@ -310,7 +380,8 @@ cs_etm_decoder__buffer_packet(struct cs_etm_packet_queue *packet_queue,
>  }
>  
>  static ocsd_datapath_resp_t
> -cs_etm_decoder__buffer_range(struct cs_etm_packet_queue *packet_queue,
> +cs_etm_decoder__buffer_range(struct cs_etm_queue *etmq,
> +			     struct cs_etm_packet_queue *packet_queue,
>  			     const ocsd_generic_trace_elem *elem,
>  			     const uint8_t trace_chan_id)
>  {
> @@ -365,6 +436,23 @@ cs_etm_decoder__buffer_range(struct cs_etm_packet_queue *packet_queue,
>  
>  	packet->last_instr_size = elem->last_instr_sz;
>  
> +	/* per-thread scenario, no need to generate a timestamp */
> +	if (cs_etm__etmq_is_timeless(etmq))
> +		goto out;
> +
> +	/*
> +	 * The packet queue is full and we haven't seen a timestamp (had we
> +	 * seen one the packet queue wouldn't be full).  Let the front end
> +	 * deal with it.
> +	 */
> +	if (ret == OCSD_RESP_WAIT)
> +		goto out;
> +
> +	packet_queue->instr_count += elem->num_instr_range;
> +	/* Tell the front end we have a new timestamp to process */
> +	ret = cs_etm_decoder__do_soft_timestamp(etmq, packet_queue,
> +						trace_chan_id);
> +out:
>  	return ret;
>  }
>  
> @@ -372,6 +460,11 @@ static ocsd_datapath_resp_t
>  cs_etm_decoder__buffer_discontinuity(struct cs_etm_packet_queue *queue,
>  				     const uint8_t trace_chan_id)
>  {
> +	/*
> +	 * Something happened and who knows when we'll get new traces so
> +	 * reset time statistics.
> +	 */
> +	cs_etm_decoder__reset_timestamp(queue);
>  	return cs_etm_decoder__buffer_packet(queue, trace_chan_id,
>  					     CS_ETM_DISCONTINUITY);
>  }
> @@ -404,6 +497,7 @@ cs_etm_decoder__buffer_exception_ret(struct cs_etm_packet_queue *queue,
>  
>  static ocsd_datapath_resp_t
>  cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
> +			struct cs_etm_packet_queue *packet_queue,
>  			const ocsd_generic_trace_elem *elem,
>  			const uint8_t trace_chan_id)
>  {
> @@ -417,6 +511,12 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq,
>  	if (cs_etm__etmq_set_tid(etmq, tid, trace_chan_id))
>  		return OCSD_RESP_FATAL_SYS_ERR;
>  
> +	/*
> +	 * A timestamp is generated after a PE_CONTEXT element so make sure
> +	 * to rely on that coming one.
> +	 */
> +	cs_etm_decoder__reset_timestamp(packet_queue);
> +
>  	return OCSD_RESP_CONT;
>  }
>  
> @@ -446,7 +546,7 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
>  							    trace_chan_id);
>  		break;
>  	case OCSD_GEN_TRC_ELEM_INSTR_RANGE:
> -		resp = cs_etm_decoder__buffer_range(packet_queue, elem,
> +		resp = cs_etm_decoder__buffer_range(etmq, packet_queue, elem,
>  						    trace_chan_id);
>  		break;
>  	case OCSD_GEN_TRC_ELEM_EXCEPTION:
> @@ -457,11 +557,15 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
>  		resp = cs_etm_decoder__buffer_exception_ret(packet_queue,
>  							    trace_chan_id);
>  		break;
> +	case OCSD_GEN_TRC_ELEM_TIMESTAMP:
> +		resp = cs_etm_decoder__do_hard_timestamp(etmq, elem,
> +							 trace_chan_id);
> +		break;
>  	case OCSD_GEN_TRC_ELEM_PE_CONTEXT:
> -		resp = cs_etm_decoder__set_tid(etmq, elem, trace_chan_id);
> +		resp = cs_etm_decoder__set_tid(etmq, packet_queue,
> +					       elem, trace_chan_id);
>  		break;
>  	case OCSD_GEN_TRC_ELEM_ADDR_NACC:
> -	case OCSD_GEN_TRC_ELEM_TIMESTAMP:
>  	case OCSD_GEN_TRC_ELEM_CYCLE_COUNT:
>  	case OCSD_GEN_TRC_ELEM_ADDR_UNKNOWN:
>  	case OCSD_GEN_TRC_ELEM_EVENT:
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 17adf554b679..91496a3a2209 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -80,6 +80,7 @@ struct cs_etm_queue {
>  	struct cs_etm_decoder *decoder;
>  	struct auxtrace_buffer *buffer;
>  	unsigned int queue_nr;
> +	u8 pending_timestamp;
>  	u64 offset;
>  	const unsigned char *buf;
>  	size_t buf_len, buf_used;
> @@ -133,6 +134,19 @@ int cs_etm__get_cpu(u8 trace_chan_id, int *cpu)
>  	return 0;
>  }
>  
> +void cs_etm__etmq_set_traceid_queue_timestamp(struct cs_etm_queue *etmq,
> +					      u8 trace_chan_id)
> +{
> +	/*
> +	 * Wnen a timestamp packet is encountered the backend code
> +	 * is stopped so that the front end has time to process packets
> +	 * that were accumulated in the traceID queue.  Since there can
> +	 * be more than one channel per cs_etm_queue, we need to specify
> +	 * what traceID queue needs servicing.
> +	 */
> +	etmq->pending_timestamp = trace_chan_id;
> +}
> +
>  static void cs_etm__clear_packet_queue(struct cs_etm_packet_queue *queue)
>  {
>  	int i;
> @@ -942,6 +956,11 @@ int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
>  	return 0;
>  }
>  
> +bool cs_etm__etmq_is_timeless(struct cs_etm_queue *etmq)
> +{
> +	return !!etmq->etm->timeless_decoding;
> +}
> +
>  static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
>  					    struct cs_etm_traceid_queue *tidq,
>  					    u64 addr, u64 period)
> diff --git a/tools/perf/util/cs-etm.h b/tools/perf/util/cs-etm.h
> index b2a7628620bf..33b57e748c3d 100644
> --- a/tools/perf/util/cs-etm.h
> +++ b/tools/perf/util/cs-etm.h
> @@ -150,6 +150,9 @@ struct cs_etm_packet_queue {
>  	u32 packet_count;
>  	u32 head;
>  	u32 tail;
> +	u32 instr_count;
> +	u64 timestamp;
> +	u64 next_timestamp;
>  	struct cs_etm_packet packet_buffer[CS_ETM_PACKET_MAX_BUFFER];
>  };
>  
> @@ -183,6 +186,9 @@ int cs_etm__process_auxtrace_info(union perf_event *event,
>  int cs_etm__get_cpu(u8 trace_chan_id, int *cpu);
>  int cs_etm__etmq_set_tid(struct cs_etm_queue *etmq,
>  			 pid_t tid, u8 trace_chan_id);
> +bool cs_etm__etmq_is_timeless(struct cs_etm_queue *etmq);
> +void cs_etm__etmq_set_traceid_queue_timestamp(struct cs_etm_queue *etmq,
> +					      u8 trace_chan_id);
>  struct cs_etm_packet_queue
>  *cs_etm__etmq_get_packet_queue(struct cs_etm_queue *etmq, u8 trace_chan_id);
>  #else
> @@ -207,6 +213,17 @@ static inline int cs_etm__etmq_set_tid(
>  	return -1;
>  }
>  
> +static inline bool cs_etm__etmq_is_timeless(
> +				struct cs_etm_queue *etmq __maybe_unused)
> +{
> +	/* What else to return? */
> +	return true;
> +}
> +
> +static inline void cs_etm__etmq_set_traceid_queue_timestamp(
> +				struct cs_etm_queue *etmq __maybe_unused,
> +				u8 trace_chan_id __maybe_unused) {}
> +
>  static inline struct cs_etm_packet_queue *cs_etm__etmq_get_packet_queue(
>  				struct cs_etm_queue *etmq __maybe_unused,
>  				u8 trace_chan_id __maybe_unused)
> -- 
> 2.17.1

-- 

- Arnaldo

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