linux-kernel - Re: [PATCH v1] perf bpf_counter: Fix opening of "any"(-1) CPU events

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Message-ID: <aOYUPWbyQv53hrjE@google.com>
Date: Wed, 8 Oct 2025 16:35:25 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Tengda Wu <wutengda@...weicloud.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf bpf_counter: Fix opening of "any"(-1) CPU events

Hi Ian,

On Tue, Oct 07, 2025 at 11:58:26AM -0700, Ian Rogers wrote:
> The bperf BPF counter code doesn't handle "any"(-1) CPU events, always
> wanting to aggregate a count against a CPU, which avoids the need for
> atomics. Force evsels used for BPF counters to require a CPU when not
> in system-wide mode so that the "any"(-1) value isn't used during map
> propagation and evsel's CPU map matches that of the PMU.
> 
> Fixes: b91917c0c6fa ("perf bpf_counter: Fix handling of cpumap fixing hybrid")
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/builtin-stat.c     | 12 ++++++++++++
>  tools/perf/util/bpf_counter.c |  1 +
>  2 files changed, 13 insertions(+)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 7006f848f87a..7fdc7f273a48 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -2797,6 +2797,18 @@ int cmd_stat(int argc, const char **argv)
>  
>  	evlist__warn_user_requested_cpus(evsel_list, target.cpu_list);
>  
> +	if (target.use_bpf && !target.system_wide) {

The target.use_bpf only checks the --bpf-counters option.  But IIUC it's
possible to use BPF only for selected events with ':b' modifier.  I
think you need to check each evsel with evsel__is_bperf().

Also system_wide might not be set for -C/--cpu option.  Probably you
want target__has_cpu() instead of target.system_wide.

Thanks,
Namhyung


> +		/*
> +		 * Setup BPF counters to require CPUs as any(-1) isn't
> +		 * supported. evlist__create_maps below will propagate this
> +		 * information to the evsels.
> +		 */
> +		struct evsel *counter;
> +
> +		evlist__for_each_entry(evsel_list, counter)
> +			counter->core.requires_cpu = true;
> +	}
> +
>  	if (evlist__create_maps(evsel_list, &target) < 0) {
>  		if (target__has_task(&target)) {
>  			pr_err("Problems finding threads of monitor\n");
> diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
> index ca5d01b9017d..d3e5933b171b 100644
> --- a/tools/perf/util/bpf_counter.c
> +++ b/tools/perf/util/bpf_counter.c
> @@ -495,6 +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;
> +	assert(!perf_cpu_map__has_any_cpu_or_is_empty(evsel->core.cpus));
>  	evsel__open(evsel, evsel->core.cpus, evsel->core.threads);
>  
>  out:
> -- 
> 2.51.0.710.ga91ca5db03-goog
>