@@ -1360,23 +1360,103 @@ 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 is used to demonstrate 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
+ * instrs_executed
+ *
+ * When the new instruction packet is coming, period
+ * instructions (Pi) contains the the number of instructions
+ * executed after the sample point(n). So for the next sample
+ * point(n+1), it is combined the two parts instructions, one
+ * is the tail of the old packet and another is the head of
+ * the new coming packet. So we use 'head' variable to cauclate
+ * the instruction numbers in the new packet for sample(n+1).
+ *
+ * For sample(n+2) and sample(n+3), they consume the instruction
+ * for sample period, so we directly generate samples based on
+ * the sampe period.
+ *
+ * After sample(n+3), there still leave some instructions which
+ * will be used by later packet; so we use 'instrs_over' to
+ * track the rest instruction number and its final value
+ * presents the tail of the packet, it will be assigned to
+ * 'tidq->period_instructions' for next round calculation.
+ */
+ u64 head, offset = 0;
+ u64 addr;
/*
- * 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)
+ * 'instrs_over' is the number of instructions executed after
+ * sample points, initialise it to 'instrs_executed' and will
+ * decrease it for consumed instructions in every synthesized
+ * instruction sample.
*/
- u64 offset = (instrs_executed - instrs_over - 1);
- u64 addr = cs_etm__instr_addr(etmq, trace_chan_id,
- tidq->packet, offset);
+ u64 instrs_over = instrs_executed;
- ret = cs_etm__synth_instruction_sample(
- etmq, tidq, addr, etm->instructions_sample_period);
- if (ret)
- return ret;
+ /*
+ * 'head' is the instructions number of the head in the new
+ * packet, it combines with the tail of previous packet to
+ * generate a sample. So 'head' uses the sample period to
+ * decrease the instruction number introduced by the previous
+ * packet.
+ */
+ head = etm->instructions_sample_period -
+ (tidq->period_instructions - instrs_executed);
+
+ if (head) {
+ offset = head;
+
+ /*
+ * 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);
+ if (ret)
+ return ret;
+
+ instrs_over -= head;
+ }
+
+ while (instrs_over >= etm->instructions_sample_period) {
+ offset += 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);
+ if (ret)
+ return ret;
+
+ instrs_over -= etm->instructions_sample_period;
+ }
/* Carry remaining instructions into next sample period */
tidq->period_instructions = instrs_over;
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 is to divide into three parts for handling coming packet: - The first part is for synthesizing the first instruction sample, it combines the instructions from the tail of previous packet and the instructions from the head of the new packet; - The second part is to simply generate samples with sample period aligned; - The third part is the tail of new packet, the rest instructions will be left to next time handling with sequential packet. Suggested-by: Mike Leach <mike.leach@linaro.org> Signed-off-by: Leo Yan <leo.yan@linaro.org> --- tools/perf/util/cs-etm.c | 106 ++++++++++++++++++++++++++++++++++----- 1 file changed, 93 insertions(+), 13 deletions(-) -- 2.17.1