Messages in this thread | | | Subject | Re: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets | From | Robert Walker <> | Date | Fri, 25 May 2018 15:03:47 +0100 |
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Hi Leo,
Following the discussions from your reply to this with a simplified patch, this version of the patch works better as you also need to emit a branch sample when handling a CS_ETM_TRACE_ON packet to indicate the end of a block of trace.
This patch does not break the output from perf inject to generate instruction samples for AutoFDO, so I am happy with that.
Regards
Rob
Reviewed-by: Robert Walker <robert.walker@arm.com>
On 22/05/18 09:39, Leo Yan wrote: > Hi Rob, > > On Mon, May 21, 2018 at 12:27:42PM +0100, Robert Walker wrote: >> Hi Leo, >> >> On 21/05/18 09:52, Leo Yan wrote: >>> Commit e573e978fb12 ("perf cs-etm: Inject capabilitity for CoreSight >>> traces") reworks the samples generation flow from CoreSight trace to >>> match the correct format so Perf report tool can display the samples >>> properly. But the change has side effect for packet handling, it only >>> generate samples when 'prev_packet->last_instr_taken_branch' is true, >>> this results in the start tracing packet and exception packets are >>> dropped. >>> >>> This patch checks extra two conditions for complete samples: >>> >>> - If 'prev_packet->sample_type' is zero we can use this condition to >>> get to know this is the start tracing packet; for this case, the start >>> packet's end_addr is zero as well so we need to handle it in the >>> function cs_etm__last_executed_instr(); >>> >> I think you also need to add something in to handle discontinuities in >> trace - for example it is possible to configure the ETM to only trace >> execution in specific code regions or to trace a few cycles every so >> often. In these cases, prev_packet->sample_type will not be zero, but >> whatever the previous packet was. You will get a CS_ETM_TRACE_ON packet in >> such cases, generated by an I_TRACE_ON element in the trace stream. >> You also get this on exception return. >> >> However, you should also keep the test for prev_packet->sample_type == 0 >> as you may not see a CS_ETM_TRACE_ON when decoding a buffer that has >> wrapped. > Thanks for reviewing. Let's dig more detailed into this issue, > especially for handling packet CS_ETM_TRACE_ON, I'd like divide into two > sub cases. > > - The first case is for using python script: > > I use python script to analyze packets with below command: > ./perf script --itrace=ril128 -s arm-cs-trace-disasm.py -F cpu,event,ip,addr,sym -- -v -d objdump -k ./vmlinux > > What I observe is after we pass python script with parameter '-s > arm-cs-trace-disasm.py', then instruction tracing options > '--itrace=ril128' isn't really used; the perf tool creates another > new process for launch python script and re-enter cmd_script() > function, but at the second time when invoke cmd_script() for python > script execution the option '--itrace=ril128' is dropped and all > parameters are only valid defined by the python script. > > As result, I can the variable 'etmq->etm->synth_opts.last_branch' is > always FALSE for running python script. So all CS_ETM_TRACE_ON > packets will be ignored in the function cs_etm__flush(). > > Even the CS_ETM_TRACE_ON packets are missed to handle, the program > flow still can work well. The reason is without the interference by > CS_ETM_TRACE_ON, the CS_ETM_RANGE packets can smoothly create > instruction range by ignore the middle CS_ETM_TRACE_ON packet. > > Please see below example, in this example there have 3 packets, the > first one packet is CS_ETM_RANGE packet which is labelled with > 'PACKET_1', the first one packet can properly generate branch sample > data with previous packet as expected; the second packet is > PACKET_2 which is CS_ETM_TRACE_ON, but > 'etmq->etm->synth_opts.last_branch' is false so function > cs_etm__flush() doesn't handle it and skip the swap operation > "etmq->prev_packet = tmp"; the third packet is PACKET_3, which is > CS_ETM_RANGE packet and we can see it's smoontly to create > continous instruction range between PACKET_1 and PACKET_3. > > cs_etm__sample: prev_packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f79c end_addr=0xffff000008a5f7bc last_instr_taken_branch=1 > PACKET_1: cs_etm__sample: packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f858 end_addr=0xffff000008a5f864 last_instr_taken_branch=1 > cs_etm__synth_branch_sample: ip=0xffff000008a5f7b8 addr=0xffff000008a5f858 pid=2290 tid=2290 id=1000000021 stream_id=1000000021 period=1 cpu=1 flags=0 cpumode=2 > > cs_etm__flush: prev_packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f858 end_addr=0xffff000008a5f864 last_instr_taken_branch=1 > PACKET_2: cs_etm__flush: packet: sample_type=2 exc=0 exc_ret=0 cpu=2 start_addr=0xdeadbeefdeadbeef end_addr=0xdeadbeefdeadbeef last_instr_taken_branch=1 > > cs_etm__sample: prev_packet: sample_type=1 exc=0 exc_ret=0 cpu=1 start_addr=0xffff000008a5f858 end_addr=0xffff000008a5f864 last_instr_taken_branch=1 > PACKET_3: cs_etm__sample: packet: sample_type=1 exc=0 exc_ret=0 cpu=2 start_addr=0xffff000008be7528 end_addr=0xffff000008be7538 last_instr_taken_branch=1 > cs_etm__synth_branch_sample: ip=0xffff000008a5f860 addr=0xffff000008be7528 pid=2290 tid=2290 id=1000000021 stream_id=1000000021 period=1 cpu=2 flags=0 cpumode=2 > > So seems to me, the CS_ETM_TRACE_ON packet doesn't introduce trouble > for the program flow analysis if we can handle all CS_ETM_RANGE > packets and without handling CS_ETM_TRACE_ON packet for branch > samples. > > - The second case is for --itrace option without python script: > ./perf script --itrace=ril -F cpu,event,ip,addr,sym -k ./vmlinux > > In this case, the flag 'etmq->etm->synth_opts.last_branch' is true > so CS_ETM_TRACE_ON packet will be handled; but I can observe the > CS_ETM_RANGE packet in etmq->prev_packet isn't handled in the > function cs_etm__flush() for branch sample, so actually we miss some > branch sample for this case. > > So I think we also need handle CS_ETM_RANGE packet in function > cs_etm__flush() to generate branch samples. But this has side > effect, we introduce the extra track for CS_ETM_TRACE_ON packet for > branch samples, so we will see one branch range like: > [ 0xdeadbeefdeadbeef .. 0xdeadbeefdeadbeef ]. > > Please reivew below change is okay for you? Thanks a lot for > suggestions. > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > index 822ba91..37d3722 100644 > --- a/tools/perf/util/cs-etm.c > +++ b/tools/perf/util/cs-etm.c > @@ -495,6 +495,13 @@ static inline void cs_etm__reset_last_branch_rb(struct cs_etm_queue *etmq) > static inline u64 cs_etm__last_executed_instr(struct cs_etm_packet *packet) > { > /* > + * The packet is the start tracing packet if the end_addr is zero, > + * returns 0 for this case. > + */ > + if (!packet->end_addr) > + return 0; > + > + /* > * The packet records the execution range with an exclusive end address > * > * A64 instructions are constant size, so the last executed > @@ -897,13 +904,28 @@ static int cs_etm__sample(struct cs_etm_queue *etmq) > etmq->period_instructions = instrs_over; > } > > - if (etm->sample_branches && > - etmq->prev_packet && > - etmq->prev_packet->sample_type == CS_ETM_RANGE && > - etmq->prev_packet->last_instr_taken_branch) { > - ret = cs_etm__synth_branch_sample(etmq); > - if (ret) > - return ret; > + if (etm->sample_branches && etmq->prev_packet) { > + bool generate_sample = false; > + > + /* Generate sample for start tracing packet */ > + if (etmq->prev_packet->sample_type == 0 || > + etmq->prev_packet->sample_type == CS_ETM_TRACE_ON) > + generate_sample = true; > + > + /* Generate sample for exception packet */ > + if (etmq->prev_packet->exc == true) > + generate_sample = true; > + > + /* Generate sample for normal branch packet */ > + if (etmq->prev_packet->sample_type == CS_ETM_RANGE && > + etmq->prev_packet->last_instr_taken_branch) > + generate_sample = true; > + > + if (generate_sample) { > + ret = cs_etm__synth_branch_sample(etmq); > + if (ret) > + return ret; > + } > } > > if (etm->sample_branches || etm->synth_opts.last_branch) { > @@ -921,12 +943,17 @@ static int cs_etm__sample(struct cs_etm_queue *etmq) > > static int cs_etm__flush(struct cs_etm_queue *etmq) > { > + struct cs_etm_auxtrace *etm = etmq->etm; > int err = 0; > struct cs_etm_packet *tmp; > > - if (etmq->etm->synth_opts.last_branch && > - etmq->prev_packet && > - etmq->prev_packet->sample_type == CS_ETM_RANGE) { > + if (!etmq->prev_packet) > + return 0; > + > + if (etmq->prev_packet->sample_type != CS_ETM_RANGE) > + return 0; > + > + if (etmq->etm->synth_opts.last_branch) { > /* > * Generate a last branch event for the branches left in the > * circular buffer at the end of the trace. > @@ -939,18 +966,25 @@ static int cs_etm__flush(struct cs_etm_queue *etmq) > err = cs_etm__synth_instruction_sample( > etmq, addr, > etmq->period_instructions); > + if (err) > + return err; > etmq->period_instructions = 0; > + } > > - /* > - * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for > - * the next incoming packet. > - */ > - tmp = etmq->packet; > - etmq->packet = etmq->prev_packet; > - etmq->prev_packet = tmp; > + if (etm->sample_branches) { > + err = cs_etm__synth_branch_sample(etmq); > + if (err) > + return err; > } > > - return err; > + /* > + * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for > + * the next incoming packet. > + */ > + tmp = etmq->packet; > + etmq->packet = etmq->prev_packet; > + etmq->prev_packet = tmp; > + return 0; > } > > static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
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