| Message ID | 20200213094204.2568-4-leo.yan@linaro.org (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | c9f5baa136777b2c982f6f7a90c9da69a88be148 |
| Headers | show |
| Series | perf cs-etm: Fix synthesizing instruction samples | expand |
Reviewed by: Mike Leach <mike.leach@linaro.org> On Thu, 13 Feb 2020 at 09:43, Leo Yan <leo.yan@linaro.org> wrote: > > 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: Mike Leach <mike.leach@linaro.org> > Signed-off-by: Leo Yan <leo.yan@linaro.org> > --- > tools/perf/util/cs-etm.c | 87 ++++++++++++++++++++++++++++++++-------- > 1 file changed, 70 insertions(+), 17 deletions(-) > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > index b2f31390126a..4b7d6c36ce3c 100644 > --- a/tools/perf/util/cs-etm.c > +++ b/tools/perf/util/cs-etm.c > @@ -1356,9 +1356,12 @@ 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 > @@ -1376,26 +1379,76 @@ 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; > > - ret = cs_etm__synth_instruction_sample( > - etmq, tidq, addr, etm->instructions_sample_period); > - if (ret) > - return ret; > + 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); > + 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) { > -- > 2.17.1 >
diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c index b2f31390126a..4b7d6c36ce3c 100644 --- a/tools/perf/util/cs-etm.c +++ b/tools/perf/util/cs-etm.c @@ -1356,9 +1356,12 @@ 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 @@ -1376,26 +1379,76 @@ 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; - ret = cs_etm__synth_instruction_sample( - etmq, tidq, addr, etm->instructions_sample_period); - if (ret) - return ret; + 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); + 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) {
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: Mike Leach <mike.leach@linaro.org> Signed-off-by: Leo Yan <leo.yan@linaro.org> --- tools/perf/util/cs-etm.c | 87 ++++++++++++++++++++++++++++++++-------- 1 file changed, 70 insertions(+), 17 deletions(-)