Re: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets

Em Fri, May 25, 2018 at 03:03:47PM +0100, Robert Walker escreveu:

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

So, Leo, can you please resubmit, bumping the v2 to v3 (or the latest one, I haven't fully reread this thread) add this "Reviewed-by: Robert" tag and any other that people may have provided, so that I can merge it?

Thanks,

- Arnaldo

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)