Re: [RFC PATCH 1/1] libperf: evlist: Fix --cpu argument on hybrid platform

[James Clark]

On 18/10/2024 00:02, Namhyung Kim wrote:
> On Tue, Oct 15, 2024 at 03:54:15PM +0100, James Clark wrote:
> > Since the linked fixes: commit, specifying a CPU on hybrid platforms
> > results in an error because Perf tries to open an extended type event
> > on "any" CPU which isn't valid. Extended type events can only be opened
> > on CPUs that match the type.
> >
> > Before (working):
> >
> >    $ perf record --cpu 1 -- true
> >    [ perf record: Woken up 1 times to write data ]
> >    [ perf record: Captured and wrote 2.385 MB perf.data (7 samples) ]
> >
> > After (not working):
> >
> >    $ perf record -C 1 -- true
> >    WARNING: A requested CPU in '1' is not supported by PMU 'cpu_atom' (CPUs 16-27) for event 'cycles:P'
> >    Error:
> >    The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cpu_atom/cycles:P/).
> >    /bin/dmesg | grep -i perf may provide additional information.
> >
> > (Ignore the warning message, that's expected and not particularly
> > relevant to this issue).
> >
> > This is because perf_cpu_map__intersect() of the user specified CPU (1)
> > and one of the PMU's CPUs (16-27) correctly results in an empty (NULL)
> > CPU map. However for the purposes of opening an event, libperf converts
> > empty CPU maps into an any CPU (-1) which the kernel rejects.
> >
> > Fix it by deleting evsels with empty CPU maps in the specific case where
> > user requested CPU maps are evaluated.
>
> I think there's a discussion about making default events skippable and
> hide them in the output unless all of them fail.
>
> Thanks,
> Namhyung

In this case it's still broken if you do -e cycles, not just for default 
events. So I'm not sure if that would help.

James