Question to perf record command

[Thomas Richter <tmricht@linux.ibm.com>]

I have a question regarding command perf record.

Command ./perf record -R -e cycles -vvv -C0 -- true
sets up perf_event_open system call with CPU == 0 and PID == -1.

According to the documentation, this applies to all processes on CPU 0
and not just the process named true.

Is this indended? I thought process true should be traced when running on 
CPU 0. Shouldn't the perf_event_open() system call in called with
CPU set to 0 and PID set to PID of process true?

Tracing output:
# ./perf record -R -e cycles -vvv -C0 -- true
DEBUGINFOD_URLS=
nr_cblocks: 0
affinity: SYS
mmap flush: 1
comp level: 0
perf record opening and mmapping events
Opening: cycles
------------------------------------------------------------
perf_event_attr:
  type                             0 (PERF_TYPE_HARDWARE)
  size                             136
  config                           0 (PERF_COUNT_HW_CPU_CYCLES)
  { sample_period, sample_freq }   4000
  sample_type                      IP|TID|TIME|ID|CPU|PERIOD|RAW
  read_format                      ID|LOST
  disabled                         1
  inherit                          1
  freq                             1
  sample_id_all                    1
  exclude_guest                    1
------------------------------------------------------------
sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8 = 5
....


When command invocation is
# ./perf record -R -e cycles -vvv -- true

the forked process named true (PID 13092) is traced on all CPUs:
[root@a35lp67 perf]# ./perf record -R -e cycles -vvv  -- true
DEBUGINFOD_URLS=
nr_cblocks: 0
affinity: SYS
mmap flush: 1
comp level: 0
perf record opening and mmapping events
Opening: cycles
------------------------------------------------------------
perf_event_attr:
  type                             0 (PERF_TYPE_HARDWARE)
  size                             136
  config                           0 (PERF_COUNT_HW_CPU_CYCLES)
  { sample_period, sample_freq }   4000
  sample_type                      IP|TID|TIME|CPU|PERIOD|RAW
  read_format                      ID|LOST
  disabled                         1
  inherit                          1
  mmap                             1
  comm                             1
  freq                             1
  enable_on_exec                   1
  task                             1
  sample_id_all                    1
  exclude_guest                    1
  mmap2                            1
  comm_exec                        1
  ksymbol                          1
  bpf_event                        1
------------------------------------------------------------
sys_perf_event_open: pid 13092  cpu 0  group_fd -1  flags 0x8 = 5
sys_perf_event_open: pid 13092  cpu 1  group_fd -1  flags 0x8 = 6
sys_perf_event_open: pid 13092  cpu 2  group_fd -1  flags 0x8 = 7
sys_perf_event_open: pid 13092  cpu 3  group_fd -1  flags 0x8 = 9
sys_perf_event_open: pid 13092  cpu 4  group_fd -1  flags 0x8 = 10
sys_perf_event_open: pid 13092  cpu 5  group_fd -1  flags 0x8 = 11
sys_perf_event_open: pid 13092  cpu 6  group_fd -1  flags 0x8 = 12
sys_perf_event_open: pid 13092  cpu 7  group_fd -1  flags 0x8 = 13
mmap size 528384B
....

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
Vorsitzender des Aufsichtsrats: Gregor Pillen
Geschäftsführung: David Faller
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294