Commit c9f5baa1 authored by Leo Yan's avatar Leo Yan Committed by Arnaldo Carvalho de Melo
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perf cs-etm: Correct synthesizing instruction samples 



When 'etm->instructions_sample_period' is less than
'tidq->period_instructions', the function cs_etm__sample() cannot handle
this case properly with its logic.

Let's see below flow as an example:

- If we set itrace option '--itrace=i4', then function cs_etm__sample()
  has variables with initialized values:

  tidq->period_instructions = 0
  etm->instructions_sample_period = 4

- When the first packet is coming:

  packet->instr_count = 10; the number of instructions executed in this
  packet is 10, thus update period_instructions as below:

  tidq->period_instructions = 0 + 10 = 10
  instrs_over = 10 - 4 = 6
  offset = 10 - 6 - 1 = 3
  tidq->period_instructions = instrs_over = 6

- When the second packet is coming:

  packet->instr_count = 10; in the second pass, assume 10 instructions
  in the trace sample again:

  tidq->period_instructions = 6 + 10 = 16
  instrs_over = 16 - 4 = 12
  offset = 10 - 12 - 1 = -3  -> the negative value
  tidq->period_instructions = instrs_over = 12

So after handle these two packets, there have below issues:

The first issue is that cs_etm__instr_addr() returns the address within
the current trace sample of the instruction related to offset, so the
offset is supposed to be always unsigned value.  But in fact, function
cs_etm__sample() might calculate a negative offset value (in handling
the second packet, the offset is -3) and pass to cs_etm__instr_addr()
with u64 type with a big positive integer.

The second issue is it only synthesizes 2 samples for sample period = 4.
In theory, every packet has 10 instructions so the two packets have
total 20 instructions, 20 instructions should generate 5 samples
(4 x 5 = 20).  This is because cs_etm__sample() only calls once
cs_etm__synth_instruction_sample() to generate instruction sample per
range packet.

This patch fixes the logic in function cs_etm__sample(); the basic
idea for handling coming packet is:

- To synthesize the first instruction sample, it combines the left
  instructions from the previous packet and the head of the new
  packet; then generate continuous samples with sample period;
- At the tail of the new packet, if it has the rest instructions,
  these instructions will be left for the sequential sample.

Suggested-by: default avatarMike Leach <mike.leach@linaro.org>
Signed-off-by: default avatarLeo Yan <leo.yan@linaro.org>
Reviewed-by: default avatarMathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: default avatarMike Leach <mike.leach@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Walker <robert.walker@arm.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: coresight ml <coresight@lists.linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lore.kernel.org/lkml/20200219021811.20067-4-leo.yan@linaro.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent f1410028

tools/perf/util/cs-etm.c

+70 −17
Original line number Diff line number Diff line
@@ -1358,9 +1358,12 @@ static int cs_etm__sample(struct cs_etm_queue *etmq, 
	struct cs_etm_auxtrace *etm = etmq->etm;

	int ret;

	u8 trace_chan_id = tidq->trace_chan_id;

	u64 instrs_executed = tidq->packet->instr_count;

	u64 instrs_prev;



	tidq->period_instructions += instrs_executed;

	/* Get instructions remainder from previous packet */

	instrs_prev = tidq->period_instructions;



	tidq->period_instructions += tidq->packet->instr_count;



	/*

	 * Record a branch when the last instruction in
@@ -1378,26 +1381,76 @@ static int cs_etm__sample(struct cs_etm_queue *etmq, 
		 * TODO: allow period to be defined in cycles and clock time

		 */



		/* Get number of instructions executed after the sample point */

		u64 instrs_over = tidq->period_instructions -

			etm->instructions_sample_period;

		/*

		 * Below diagram demonstrates the instruction samples

		 * generation flows:

		 *

		 *    Instrs     Instrs       Instrs       Instrs

		 *   Sample(n)  Sample(n+1)  Sample(n+2)  Sample(n+3)

		 *    |            |            |            |

		 *    V            V            V            V

		 *   --------------------------------------------------

		 *            ^                                  ^

		 *            |                                  |

		 *         Period                             Period

		 *    instructions(Pi)                   instructions(Pi')

		 *

		 *            |                                  |

		 *            \---------------- -----------------/

		 *                             V

		 *                 tidq->packet->instr_count

		 *

		 * Instrs Sample(n...) are the synthesised samples occurring

		 * every etm->instructions_sample_period instructions - as

		 * defined on the perf command line.  Sample(n) is being the

		 * last sample before the current etm packet, n+1 to n+3

		 * samples are generated from the current etm packet.

		 *

		 * tidq->packet->instr_count represents the number of

		 * instructions in the current etm packet.

		 *

		 * Period instructions (Pi) contains the the number of

		 * instructions executed after the sample point(n) from the

		 * previous etm packet.  This will always be less than

		 * etm->instructions_sample_period.

		 *

		 * When generate new samples, it combines with two parts

		 * instructions, one is the tail of the old packet and another

		 * is the head of the new coming packet, to generate

		 * sample(n+1); sample(n+2) and sample(n+3) consume the

		 * instructions with sample period.  After sample(n+3), the rest

		 * instructions will be used by later packet and it is assigned

		 * to tidq->period_instructions for next round calculation.

		 */



		/*

		 * Calculate the address of the sampled instruction (-1 as

		 * sample is reported as though instruction has just been

		 * executed, but PC has not advanced to next instruction)

		 * Get the initial offset into the current packet instructions;

		 * entry conditions ensure that instrs_prev is less than

		 * etm->instructions_sample_period.

		 */

		u64 offset = (instrs_executed - instrs_over - 1);

		u64 addr = cs_etm__instr_addr(etmq, trace_chan_id,

					      tidq->packet, offset);

		u64 offset = etm->instructions_sample_period - instrs_prev;

		u64 addr;



		while (tidq->period_instructions >=

				etm->instructions_sample_period) {

			/*

			 * Calculate the address of the sampled instruction (-1

			 * as sample is reported as though instruction has just

			 * been executed, but PC has not advanced to next

			 * instruction)

			 */

			addr = cs_etm__instr_addr(etmq, trace_chan_id,

						  tidq->packet, offset - 1);

			ret = cs_etm__synth_instruction_sample(

			etmq, tidq, addr, etm->instructions_sample_period);

				etmq, tidq, addr,

				etm->instructions_sample_period);

			if (ret)

				return ret;



		/* Carry remaining instructions into next sample period */

		tidq->period_instructions = instrs_over;

			offset += etm->instructions_sample_period;

			tidq->period_instructions -=

				etm->instructions_sample_period;

		}

	}



	if (etm->sample_branches) {

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