Re: [PATCHv3] perf stat: Ensure group is defined on top of the same cpu mask

[Arnaldo Carvalho de Melo]

Em Tue, Jun 02, 2020 at 04:05:08PM +0200, Jiri Olsa escreveu:
> On Tue, Jun 02, 2020 at 10:42:56AM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Jun 02, 2020 at 12:17:36PM +0200, Jiri Olsa escreveu:
> > > Jin Yao reported the issue (and posted first versions of this change)
> > > with groups being defined over events with different cpu mask.
> >
> > > This causes assert aborts in get_group_fd, like:
> >
> > >   # perf stat -M "C2_Pkg_Residency" -a -- sleep 1
> > >   perf: util/evsel.c:1464: get_group_fd: Assertion `!(fd == -1)' failed.
> > >   Aborted
> >
> > > All the events in the group have to be defined over the same
> > > cpus so the group_fd can be found for every leader/member pair.
> >
> > > Adding check to ensure this condition is met and removing the
> > > group (with warning) if we detect mixed cpus, like:
> >
> > >   $ sudo perf stat -e '{power/energy-cores/,cycles},{instructions,power/energy-cores/}'
> > >   WARNING: event cpu maps do not match, disabling group:
> > >     anon group { power/energy-cores/, cycles }
> > >     anon group { instructions, power/energy-cores/ }
> >
> > So it doesn't disable the 'group', it disables the 'grouping' of those
> > events, right? I.e. reading the WARNING, I thought that it would count
> > nothing, since it lists both groups as being disabled, but when I tested
> > I noticed that:
> >
> >   [root@seventh ~]# perf stat -e '{power/energy-cores/,cycles},{instructions,power/energy-cores/}'
> >   WARNING: grouped events cpus do not match, disabling group:
> >     anon group { power/energy-cores/, cycles }
> >     anon group { instructions, power/energy-cores/ }
> >   ^C
> >    Performance counter stats for 'system wide':
> >
> >                12.62 Joules power/energy-cores/
> >          106,920,637        cycles
> >           80,228,899        instructions              #    0.75  insn per cycle
> >                12.62 Joules power/energy-cores/
> >
> >         14.514476987 seconds time elapsed
> >
> >
> >   [root@seventh ~]#
> >
> >   I.e. it counted the events, ungrouped, or am I missing something?
>
> right, it disables 'grouping', events are scheduled/counted individualy

Ok, I applied this already, we can fix this in the next cycle.

> this way we will not hit the issue when looking for group_fd FD
> and there's not any, because of different cpu maps

> > If I do:

> >   [root@seventh ~]# perf stat -e '{power/energy-cores/,power/energy-ram/},{instructions,cycles}' -a sleep 2

> >    Performance counter stats for 'system wide':

> >                 1.73 Joules power/energy-cores/
> >                 0.92 Joules power/energy-ram/
> >           12,191,658        instructions              #    0.67  insn per cycles/
> >           18,275,233        cycles

> >          2.001272492 seconds time elapsed

> >   [root@seventh ~]#
> >
> > It works, grouped. One observation, shouldn't we somehow show in the
> > output that the first two were indeed grouped, ditto for the second two?

> yea, we don't display groups in output.. also there's no number
> for the group, it's still separate events numbers in output
> grouping is only used when creating events

perhaps if we just add a blank line to separate groups? I.e. the above
would be:

[root@seventh ~]# perf stat -e '{power/energy-cores/,power/energy-ram/},{instructions,cycles}' -a sleep 2

 Performance counter stats for 'system wide':

              1.73 Joules power/energy-cores/
              0.92 Joules power/energy-ram/

        12,191,658        instructions              #    0.67  insn per cycle
        18,275,233        cycles

       2.001272492 seconds time elapsed

[root@seventh ~]#

Humm, in the presence of at least one group, any ungrouped events would
have to be also separated, i.e.:

[root@seventh ~]# perf stat -e '{power/energy-cores/,power/energy-ram/},instructions,cycles' -a sleep 2

 Performance counter stats for 'system wide':

              1.73 Joules power/energy-cores/
              0.92 Joules power/energy-ram/

        12,191,658        instructions              #    0.67  insn per cycle

        18,275,233        cycles

       2.001272492 seconds time elapsed

[root@seventh ~]#

wdyt?

> > Also, this needs improvement:

> >   [root@seventh ~]# perf stat -e '{power/energy-cores/,power/energy-ram/},{instructions,cycles}' sleep 2
> >   Error:
> >   The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (power/energy-cores/).
> >   /bin/dmesg | grep -i perf may provide additional information.

> yes, power events don't work with events without cpu being defined,
> which is what we do for 'workload' session.. we should either check
> for that and display some sensible error for power events

> or perhaps check if we could monitor like perf record does with creating
> events for task and every cpu in the system

- Arnaldo