Re: [BUG] perf: No samples found when using kcore + coresight

[Leo Yan]

On Thu, Mar 09, 2023 at 10:06:41AM -0800, Yang Shi wrote:

[...]

> > I reviewed your shared dump, the bad and good perf data both contain the
> > dummy event with 'text_poke = 1'.  Could you confirm the shared dump in
> > your previous email is correct or not?
> 
> Oops, sorry. I pasted the wrong log. The good one looks like
> (generated by v5.19):
> 
> # captured on    : Wed Mar  8 18:02:58 2023
> # header version : 1
> # data offset    : 408
> # data size      : 22640
> # feat offset    : 23048
> # hostname : fedora
> # os release : 6.2.0-coresight+
> # perf version : 5.19.g3d7cb6b04c3f
> # arch : aarch64
> # nrcpus online : 128
> # nrcpus avail : 128
> # cpuid : 0x00000000c00fac30
> # total memory : 2108862504 kB
> # cmdline : /home/yshi/linux/tools/perf/perf record -e
> cs_etm/@tmc_etf63/k --kcore --per-thread -- taskset --cpu-list 1 uname
> # event : name = cs_etm/@tmc_etf63/k, , id = { 3832 }, type = 9, size
> = 128, { sample_period, sample_freq } = 1, sample_type =
> IP|TID|IDENTIFIER, read_format = ID, d
> isabled = 1, exclude_user = 1, exclude_hv = 1, enable_on_exec = 1,
> sample_id_all = 1, { bp_len, config2 } = 0x12792918
> # event : name = dummy:u, , id = { 3833 }, type = 1, size = 128,
> config = 0x9, { sample_period, sample_freq } = 1, sample_type =
> IP|TID|IDENTIFIER, read_format = ID,
>  disabled = 1, exclude_kernel = 1, exclude_hv = 1, mmap = 1, comm = 1,
> enable_on_exec = 1, task = 1, sample_id_all = 1, exclude_guest = 1,
> mmap2 = 1, comm_exec = 1,
> context_switch = 1, ksymbol = 1, bpf_event = 1
> # CPU_TOPOLOGY info available, use -I to display
> # NUMA_TOPOLOGY info available, use -I to display
> # pmu mappings: armv8_pmuv3_0 = 8, software = 1, arm_cmn_0 = 10,
> uprobe = 7, cs_etm = 9, breakpoint = 5, tracepoint = 2, arm_cmn_1 =
> 11, kprobe = 6
> # contains AUX area data (e.g. instruction trace)
> # CACHE info available, use -I to display
> # time of first sample : 18446744073.709551
> # time of last sample : 18446744073.709551
> # sample duration :      0.000 ms
> # MEM_TOPOLOGY info available, use -I to display
> # missing features: TRACING_DATA CPUDESC BRANCH_STACK GROUP_DESC STAT
> CLOCKID DIR_FORMAT COMPRESSED CPU_PMU_CAPS CLOCK_DATA HYBRID_TOPOLOGY
> HYBRID_CPU_PMU_CAPS

Thanks for confirmation.

Just a quick summary, here we have two issues:

- With command:
  perf record -e cs_etm/@tmc_etf63/k --kcore --per-thread \
  -- taskset --cpu-list 1 uname",

  perf doesn't enable "text poke" attribution.

- With command:
  perf record -e cs_etm/@tmc_etf63/k --kcore --per-thread \
  -- taskset --cpu-list 1 true (in your previous email), or ...
  perf record --kcore -e cs_etm/@tmc_etf63/k --per-thread \
  -- taskset --cpu-list 1 uname (in your shared perf data file),

  perf enables "text poke" attribution, in this case, perf fails to decode
  Arm CoreSight trace data.

[...]

> > Do you mind to share the bad perf.data file with James and me?
> 
> Please check the attachment out. Thanks for looking into this problem.

Thank you for sharing the data.  We will look into it.

Leo