linux-kernel - Re: [PATCH V2 00/23] perf intel-pt: Better support for perf record --cpu

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Date:   Mon, 9 May 2022 16:46:17 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ian Rogers <irogers@...gle.com>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, James Clark <James.Clark@....com>,
        German Gomez <german.gomez@....com>
Subject: Re: [PATCH V2 00/23] perf intel-pt: Better support for perf record
 --cpu

On Mon, May 09, 2022 at 08:44:02AM +0300, Adrian Hunter wrote:

[...]

> > Thanks a lot for this patch set, I believe this is a common issue for
> > AUX trace (not only for Intel-PT), so I verified this patch set for both
> > Arm CoreSight and SPE; unfortunately both cannot see MMAP events for
> > migrated task.  I used below commands:
> > 
> >   # perf record -B -N --no-bpf-event -e cs_etm//u -C 0 -- taskset --cpu-list 1 uname
> >   # perf script  --no-itrace --show-mmap-events -C 1 2>/dev/null | grep MMAP | wc -l
> >   0
> > 
> > 
> >   # perf record -B -N --no-bpf-event -e arm_spe_0//u -C 0 -- taskset --cpu-list 1 uname
> >   # perf script --no-itrace --show-mmap-events -C 1 2>/dev/null | grep MMAP | wc -l
> >   0
> > 
> > I didn't dive into details for this patch set, so I cannot say the
> > failure is caused by any issue in this patch set.  But it's definitely
> > we need to look into for Arm platforms to root cause what's the reason
> > it cannot record MMAP events properly when migrate tasks.  Loop James
> > and German for this reason.
> 
> You would need the equivalent of patch "perf intel-pt: Track sideband
> system-wide when needed" which makes use of new helper
> evlist__add_aux_dummy() to set up the dummy event with the option to
> make it "system wide".
> 
> cs_etm_recording_options() and arm_spe_recording_options() have similar
> code.

Thanks a lot for the guidance.

I applied the simliar change for cs_etm_recording_options() and
arm_spe_recording_options(), both can pass below tests:

  # perf record -B -N --no-bpf-event -e cs_etm//u -C 0 -- taskset --cpu-list 1 uname
  # perf script  --no-itrace --show-mmap-events -C 1 2>/dev/null | grep MMAP | wc -l
  4

  # perf record -B -N --no-bpf-event -e arm_spe_0//u -C 0 -- taskset --cpu-list 1 uname
  # perf script --no-itrace --show-mmap-events -C 1 2>/dev/null | grep MMAP | wc -l      
  4

And I tested a more complex case for migrating a test program 'sysbench'
in the middle of perf session, it still fails to parse any samples
testing program 'sysbench'.  I need to do more homework for this part,
but welcome any suggestions, thanks!  The testing script is:

---8<---

export PATH=/mnt/export/arm-linux-kernel/tools/perf/:$PATH

perf record --kcore -C 1 -e cs_etm// &
PERF_PID=$!
echo "Perf PID ${PERF_PID}"

sleep 2

taskset 0x1 ./sysbench --test=memory --max-requests=1000000000 run &
TEST_PROG_PID=$!
echo "Test Prog PID ${TEST_PROG_PID}"

sleep 1

taskset -p 0x2 $TEST_PROG_PID

sleep 1

kill $PERF_PID

> You will need to decide if it is worth the extra sideband.  I decided
> if it became an issue, it could be made optional in the future.

Yeah, the condition checking for system wide tracking in patch 16/23
looks good to me.

Thanks,
Leo