Re: [PATCH v1 2/2] perf bpf_counter: Fix handling of cpumap fixing hybrid

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Mon, Oct 06, 2025 at 09:18:22AM -0700, Ian Rogers wrote:
> On Wed, Oct 1, 2025 at 11:12 AM Ian Rogers <irogers@google.com> wrote:
> >
> > Don't open evsels on all CPUs, open them just on the CPUs they
> > support. This avoids opening say an e-core event on a p-core and
> > getting a failure - achieve this by getting rid of the "all_cpu_map".
> >
> > In install_pe functions don't use the cpu_map_idx as a CPU number,
> > translate the cpu_map_idx, which is a dense index into the cpu_map
> > skipping holes at the beginning, to a proper CPU number.
> >
> > Before:
> > ```
> > $ perf stat --bpf-counters -a -e cycles,instructions -- sleep 1
> >
> >  Performance counter stats for 'system wide':
> >
> >    <not supported>      cpu_atom/cycles/
> >        566,270,672      cpu_core/cycles/
> >    <not supported>      cpu_atom/instructions/
> >        572,792,836      cpu_core/instructions/           #    1.01  insn per cycle
> >
> >        1.001595384 seconds time elapsed
> > ```
> >
> > After:
> > ```
> > $ perf stat --bpf-counters -a -e cycles,instructions -- sleep 1
> >
> >  Performance counter stats for 'system wide':
> >
> >        443,299,201      cpu_atom/cycles/
> >      1,233,919,737      cpu_core/cycles/
> >        213,634,112      cpu_atom/instructions/           #    0.48  insn per cycle
> >      2,758,965,527      cpu_core/instructions/           #    2.24  insn per cycle
> >
> >        1.001699485 seconds time elapsed
> > ```
> >
> > Fixes: 7fac83aaf2ee ("perf stat: Introduce 'bperf' to share hardware PMCs with BPF")
> > Signed-off-by: Ian Rogers <irogers@google.com>
> 
> +Thomas Falcon
> 
> I think it'd be nice to get this quite major fix for
> --bpf-counters/bperf for hybrid architectures into v6.18 and stable
> builds. Thomas would it be possible for you to give a Tested-by tag
> using the reproduction in the commit message?

Its even already in linux-next:

⬢ [acme@toolbx perf-tools-next]$ git log -5 --oneline linux-next/master tools/perf/util/bpf_counter.c
b91917c0c6fa6df9 perf bpf_counter: Fix handling of cpumap fixing hybrid
8c519a825b4add85 perf bpf_counter: Move header declarations into C code
07dc3a6de33098b0 perf stat: Support inherit events during fork() for bperf
effe957c6bb70cac libperf cpumap: Replace usage of perf_cpu_map__new(NULL) with perf_cpu_map__new_online_cpus()
b84b3f47921568a8 perf bpf_counter: Fix a few memory leaks
⬢ [acme@toolbx perf-tools-next]$