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

[Yang Shi]

On Mon, Mar 13, 2023 at 5:14 AM Leo Yan <leo.yan at linaro.org> wrote:
>
> 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.

No, it enables "text poke" and perf fails to decode coresight trace
data too. It doesn't matter whether "--kcore" is after or before "-e
cs/etm/@tmc_etf63/k".

>
> - 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.

Yes.

>
> [...]
>
> > > 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.

Thank you.

>
> Leo