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(-)
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c index 8be6d010ae84..8e9eb7583bcd 100644 --- a/tools/perf/util/cs-etm.c +++ b/tools/perf/util/cs-etm.c @@ -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;