Re: [PATCH v1 2/2] perf bpf_counter: Fix handling of cpumap fixing hybrid
From: Falcon, Thomas
Date: Mon Oct 06 2025 - 16:48:06 EST
On Mon, 2025-10-06 at 09:18 -0700, Ian Rogers wrote:
> On Wed, Oct 1, 2025 at 11:12 AM Ian Rogers <irogers@xxxxxxxxxx>
> 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@xxxxxxxxxx>
>
> +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?
>
> Thanks,
> Ian
>
Sorry for missing this. Here's my reproduction on an alder lake
sudo ./perf stat --bpf-counters -a -e cycles,instructions -- sleep 1
...
Performance counter stats for 'system wide':
364,715,896 cpu_atom/cycles/
946,331,957 cpu_core/cycles/
169,842,929 cpu_atom/instructions/ # 0.47
insn per cycle
1,338,720,324 cpu_core/instructions/ # 1.41
insn per cycle
1.001667769 seconds time elapsed
It looks like it's in perf-tools-next already but have my tested by for
what it's worth.
Tested-by: Thomas Falcon <thomas.falcon@xxxxxxxxx>
> > ---
> > tools/perf/util/bpf_counter.c | 26 ++++++++++--------------
> > --
> > tools/perf/util/bpf_counter_cgroup.c | 3 ++-
> > 2 files changed, 12 insertions(+), 17 deletions(-)
> >
> > diff --git a/tools/perf/util/bpf_counter.c
> > b/tools/perf/util/bpf_counter.c
> > index 1c6cb5ea077e..ca5d01b9017d 100644
> > --- a/tools/perf/util/bpf_counter.c
> > +++ b/tools/perf/util/bpf_counter.c
> > @@ -336,6 +336,7 @@ static int
> > bpf_program_profiler__install_pe(struct evsel *evsel, int
> > cpu_map_idx
> > {
> > struct bpf_prog_profiler_bpf *skel;
> > struct bpf_counter *counter;
> > + int cpu = perf_cpu_map__cpu(evsel->core.cpus,
> > cpu_map_idx).cpu;
> > int ret;
> >
> > list_for_each_entry(counter, &evsel->bpf_counter_list,
> > list) {
> > @@ -343,7 +344,7 @@ static int
> > bpf_program_profiler__install_pe(struct evsel *evsel, int
> > cpu_map_idx
> > assert(skel != NULL);
> >
> > ret = bpf_map_update_elem(bpf_map__fd(skel-
> > >maps.events),
> > - &cpu_map_idx, &fd,
> > BPF_ANY);
> > + &cpu, &fd, BPF_ANY);
> > if (ret)
> > return ret;
> > }
> > @@ -451,7 +452,6 @@ static int bperf_check_target(struct evsel
> > *evsel,
> > return 0;
> > }
> >
> > -static struct perf_cpu_map *all_cpu_map;
> > static __u32 filter_entry_cnt;
> >
> > static int bperf_reload_leader_program(struct evsel *evsel, int
> > attr_map_fd,
> > @@ -495,7 +495,7 @@ static int bperf_reload_leader_program(struct
> > evsel *evsel, int attr_map_fd,
> > * following evsel__open_per_cpu call
> > */
> > evsel->leader_skel = skel;
> > - evsel__open_per_cpu(evsel, all_cpu_map, -1);
> > + evsel__open(evsel, evsel->core.cpus, evsel->core.threads);
> >
> > out:
> > bperf_leader_bpf__destroy(skel);
> > @@ -533,12 +533,6 @@ static int bperf__load(struct evsel *evsel,
> > struct target *target)
> > if (bperf_check_target(evsel, target, &filter_type,
> > &filter_entry_cnt))
> > return -1;
> >
> > - if (!all_cpu_map) {
> > - all_cpu_map = perf_cpu_map__new_online_cpus();
> > - if (!all_cpu_map)
> > - return -1;
> > - }
> > -
> > evsel->bperf_leader_prog_fd = -1;
> > evsel->bperf_leader_link_fd = -1;
> >
> > @@ -656,9 +650,10 @@ static int bperf__load(struct evsel *evsel,
> > struct target *target)
> > static int bperf__install_pe(struct evsel *evsel, int cpu_map_idx,
> > int fd)
> > {
> > struct bperf_leader_bpf *skel = evsel->leader_skel;
> > + int cpu = perf_cpu_map__cpu(evsel->core.cpus,
> > cpu_map_idx).cpu;
> >
> > return bpf_map_update_elem(bpf_map__fd(skel->maps.events),
> > - &cpu_map_idx, &fd, BPF_ANY);
> > + &cpu, &fd, BPF_ANY);
> > }
> >
> > /*
> > @@ -667,13 +662,12 @@ static int bperf__install_pe(struct evsel
> > *evsel, int cpu_map_idx, int fd)
> > */
> > static int bperf_sync_counters(struct evsel *evsel)
> > {
> > - int num_cpu, i, cpu;
> > + struct perf_cpu cpu;
> > + int idx;
> > +
> > + perf_cpu_map__for_each_cpu(cpu, idx, evsel->core.cpus)
> > + bperf_trigger_reading(evsel->bperf_leader_prog_fd,
> > cpu.cpu);
> >
> > - num_cpu = perf_cpu_map__nr(all_cpu_map);
> > - for (i = 0; i < num_cpu; i++) {
> > - cpu = perf_cpu_map__cpu(all_cpu_map, i).cpu;
> > - bperf_trigger_reading(evsel->bperf_leader_prog_fd,
> > cpu);
> > - }
> > return 0;
> > }
> >
> > diff --git a/tools/perf/util/bpf_counter_cgroup.c
> > b/tools/perf/util/bpf_counter_cgroup.c
> > index ed6a29b106b4..690be3ce3e11 100644
> > --- a/tools/perf/util/bpf_counter_cgroup.c
> > +++ b/tools/perf/util/bpf_counter_cgroup.c
> > @@ -186,7 +186,8 @@ static int bperf_cgrp__load(struct evsel
> > *evsel,
> > }
> >
> > static int bperf_cgrp__install_pe(struct evsel *evsel
> > __maybe_unused,
> > - int cpu __maybe_unused, int fd
> > __maybe_unused)
> > + int cpu_map_idx __maybe_unused,
> > + int fd __maybe_unused)
> > {
> > /* nothing to do */
> > return 0;
> > --
> > 2.51.0.618.g983fd99d29-goog
> >