When AUX area events are used in sampling mode, they must be the group
leader, but the group leader is also used for leader-sampling. However,
it is not desirable to use an AUX area event as the leader for
leader-sampling, because it doesn't have any samples of its own. To support
leader-sampling with AUX area events, use the 2nd event of the group as the
"leader" for the purposes of leader-sampling.

Example:

 # perf record --kcore --aux-sample -e '{intel_pt//,cycles,instructions}:S' -c 10000 uname
 [ perf record: Woken up 3 times to write data ]
 [ perf record: Captured and wrote 0.786 MB perf.data ]
 # perf report
 Samples: 380  of events 'anon group { cycles, instructions }', Event count (approx.): 3026164
           Children              Self  Command  Shared Object      Symbol
 +   38.76%  42.65%     0.00%   0.00%  uname    [kernel.kallsyms]  [k] __x86_indirect_thunk_rax
 +   35.82%  31.33%     0.00%   0.00%  uname    ld-2.28.so         [.] _dl_start_user
 +   34.29%  29.74%     0.55%   0.47%  uname    ld-2.28.so         [.] _dl_start
 +   33.73%  28.62%     1.60%   0.97%  uname    ld-2.28.so         [.] dl_main
 +   33.19%  29.04%     0.52%   0.32%  uname    ld-2.28.so         [.] _dl_sysdep_start
 +   27.83%  33.74%     0.00%   0.00%  uname    [kernel.kallsyms]  [k] do_syscall_64
 +   26.76%  33.29%     0.00%   0.00%  uname    [kernel.kallsyms]  [k] entry_SYSCALL_64_after_hwframe
 +   23.78%  20.33%     5.97%   5.25%  uname    [kernel.kallsyms]  [k] page_fault
 +   23.18%  24.60%     0.00%   0.00%  uname    libc-2.28.so       [.] __libc_start_main
 +   22.64%  24.37%     0.00%   0.00%  uname    uname              [.] _start
 +   21.04%  23.27%     0.00%   0.00%  uname    uname              [.] main
 +   19.48%  18.08%     3.72%   3.64%  uname    ld-2.28.so         [.] _dl_relocate_object
 +   19.47%  21.81%     0.00%   0.00%  uname    libc-2.28.so       [.] setlocale
 +   19.44%  21.56%     0.52%   0.61%  uname    libc-2.28.so       [.] _nl_find_locale
 +   17.87%  19.66%     0.00%   0.00%  uname    libc-2.28.so       [.] _nl_load_locale_from_archive
 +   15.71%  13.73%     0.53%   0.52%  uname    [kernel.kallsyms]  [k] do_page_fault
 +   15.18%  13.21%     1.03%   0.68%  uname    [kernel.kallsyms]  [k] handle_mm_fault
 +   14.15%  12.53%     1.01%   1.12%  uname    [kernel.kallsyms]  [k] __handle_mm_fault
 +   12.03%   9.67%     0.54%   0.32%  uname    ld-2.28.so         [.] _dl_map_object
 +   10.55%   8.48%     0.00%   0.00%  uname    ld-2.28.so         [.] openaux
 +   10.55%  20.20%     0.52%   0.61%  uname    libc-2.28.so       [.] __run_exit_handlers

Comnmitter notes:

Fixed up this problem:

  util/record.c: In function ‘perf_evlist__config’:
  util/record.c:256:3: error: too few arguments to function ‘perf_evsel__config_leader_sampling’
    256 |   perf_evsel__config_leader_sampling(evsel);
        |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  util/record.c:190:13: note: declared here
    190 | static void perf_evsel__config_leader_sampling(struct evsel *evsel,
        |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/20200401101613.6201-17-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>