linux-kernel - Re: [PATCH v4] perf test: Introduce script for data symbol testing

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Date:   Sat, 1 Oct 2022 10:43:10 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Namhyung Kim <namhyung@...nel.org>, Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v4] perf test: Introduce script for data symbol testing

>> +# perf mem/c2c internally uses IBS PMU on AMD CPU which doesn't support
>> +# user/kernel filtering and per-process monitoring, spin program on
>> +# specific CPU and test in per-CPU mode.
>> +is_amd=$(egrep -c 'vendor_id.*AuthenticAMD' /proc/cpuinfo)
>> +if (($is_amd >= 1)); then
>> +       perf mem record -o ${PERF_DATA} -- -C 0 -- taskset -c 0 $TEST_PROGRAM &
> 
> I'm curious why it has "--" before "-C 0"..

IIRC, any command line options placed after -- will be carry forwarded
as is to perf record.

perf mem record [options] does not support -C option. Which means -C 0
will be ignored if user run `perf mem record -C 0`. Ex:

  $ sudo ./perf --debug perf-event-open mem record -C 0
  [...]
  sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0 = 5
  sys_perf_event_open: pid -1  cpu 1  group_fd -1  flags 0 = 6
  sys_perf_event_open: pid -1  cpu 2  group_fd -1  flags 0 = 7
  sys_perf_event_open: pid -1  cpu 3  group_fd -1  flags 0 = 8

OTOH, if I place -C 0 after -- then perf opens event only on cpu0:

  $ sudo ./perf --debug perf-event-open mem record -- -C 0
  [...]
  sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0 = 7

Now, perf mem [options] supports -C options but I don't know why
it's not working for me:

  $ sudo ./perf --debug perf-event-open mem -C 0 record
  [...]
  sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0 = 5
  sys_perf_event_open: pid -1  cpu 1  group_fd -1  flags 0 = 6
  sys_perf_event_open: pid -1  cpu 2  group_fd -1  flags 0 = 7
  sys_perf_event_open: pid -1  cpu 3  group_fd -1  flags 0 = 8

Thanks,
Ravi