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Message-ID: <f28577c1-ca95-43ca-b179-32e2cd46d054@arm.com>
Date: Thu, 4 Dec 2025 12:48:53 +0000
From: Christian Loehle <christian.loehle@....com>
To: Samuel Wu <wusamuel@...gle.com>, Huang Rui <ray.huang@....com>,
"Gautham R. Shenoy" <gautham.shenoy@....com>,
Mario Limonciello <mario.limonciello@....com>,
Perry Yuan <perry.yuan@....com>, Jonathan Corbet <corbet@....net>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>, Steven Rostedt
<rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Len Brown <lenb@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
<eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>,
James Clark <james.clark@...aro.org>
Cc: kernel-team@...roid.com, linux-pm@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v3 1/2] cpufreq: Replace trace_cpu_frequency with
trace_policy_frequency
On 12/1/25 20:24, Samuel Wu wrote:
> The existing cpu_frequency trace_event can be verbose, emitting a nearly
> identical trace event for every CPU in the policy even when their
> frequencies are identical.
>
> This patch replaces the cpu_frequency trace event with policy_frequency
> trace event, a more efficient alternative. From the kernel's
> perspective, emitting a trace event once per policy instead of once per
> cpu saves some memory and is less overhead. From the post-processing
> perspective, analysis of the trace log is simplified without any loss of
> information.
>
> Signed-off-by: Samuel Wu <wusamuel@...gle.com>
> ---
> drivers/cpufreq/cpufreq.c | 14 ++------------
> drivers/cpufreq/intel_pstate.c | 6 ++++--
> include/trace/events/power.h | 24 +++++++++++++++++++++---
> kernel/trace/power-traces.c | 2 +-
> samples/bpf/cpustat_kern.c | 8 ++++----
> samples/bpf/cpustat_user.c | 6 +++---
> tools/perf/builtin-timechart.c | 12 ++++++------
> 7 files changed, 41 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 4472bb1ec83c..dd3f08f3b958 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -309,8 +309,6 @@ static void cpufreq_notify_transition(struct cpufreq_policy *policy,
> struct cpufreq_freqs *freqs,
> unsigned int state)
> {
> - int cpu;
> -
> BUG_ON(irqs_disabled());
>
> if (cpufreq_disabled())
> @@ -344,10 +342,7 @@ static void cpufreq_notify_transition(struct cpufreq_policy *policy,
> adjust_jiffies(CPUFREQ_POSTCHANGE, freqs);
> pr_debug("FREQ: %u - CPUs: %*pbl\n", freqs->new,
> cpumask_pr_args(policy->cpus));
> -
> - for_each_cpu(cpu, policy->cpus)
> - trace_cpu_frequency(freqs->new, cpu);
> -
> + trace_policy_frequency(freqs->new, policy->cpu, policy->cpus);
> srcu_notifier_call_chain(&cpufreq_transition_notifier_list,
> CPUFREQ_POSTCHANGE, freqs);
>
> @@ -2201,7 +2196,6 @@ unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
> unsigned int target_freq)
> {
> unsigned int freq;
> - int cpu;
>
> target_freq = clamp_val(target_freq, policy->min, policy->max);
> freq = cpufreq_driver->fast_switch(policy, target_freq);
> @@ -2213,11 +2207,7 @@ unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
> arch_set_freq_scale(policy->related_cpus, freq,
> arch_scale_freq_ref(policy->cpu));
> cpufreq_stats_record_transition(policy, freq);
> -
> - if (trace_cpu_frequency_enabled()) {
> - for_each_cpu(cpu, policy->cpus)
> - trace_cpu_frequency(freq, cpu);
> - }
> + trace_policy_frequency(freq, policy->cpu, policy->cpus);
>
> return freq;
> }
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index ec4abe374573..9724b5d19d83 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -2297,7 +2297,8 @@ static int hwp_get_cpu_scaling(int cpu)
>
> static void intel_pstate_set_pstate(struct cpudata *cpu, int pstate)
> {
> - trace_cpu_frequency(pstate * cpu->pstate.scaling, cpu->cpu);
> + trace_policy_frequency(pstate * cpu->pstate.scaling, cpu->cpu,
> + cpumask_of(cpu->cpu));
> cpu->pstate.current_pstate = pstate;
> /*
> * Generally, there is no guarantee that this code will always run on
> @@ -2587,7 +2588,8 @@ static void intel_pstate_adjust_pstate(struct cpudata *cpu)
>
> target_pstate = get_target_pstate(cpu);
> target_pstate = intel_pstate_prepare_request(cpu, target_pstate);
> - trace_cpu_frequency(target_pstate * cpu->pstate.scaling, cpu->cpu);
> + trace_policy_frequency(target_pstate * cpu->pstate.scaling, cpu->cpu,
> + cpumask_of(cpu->cpu));
> intel_pstate_update_pstate(cpu, target_pstate);
>
> sample = &cpu->sample;
> diff --git a/include/trace/events/power.h b/include/trace/events/power.h
> index 370f8df2fdb4..317098ffdd5f 100644
> --- a/include/trace/events/power.h
> +++ b/include/trace/events/power.h
> @@ -182,11 +182,29 @@ TRACE_EVENT(pstate_sample,
> { PM_EVENT_RECOVER, "recover" }, \
> { PM_EVENT_POWEROFF, "poweroff" })
>
> -DEFINE_EVENT(cpu, cpu_frequency,
> +TRACE_EVENT(policy_frequency,
>
> - TP_PROTO(unsigned int frequency, unsigned int cpu_id),
> + TP_PROTO(unsigned int frequency, unsigned int cpu_id,
> + const struct cpumask *policy_cpus),
>
> - TP_ARGS(frequency, cpu_id)
> + TP_ARGS(frequency, cpu_id, policy_cpus),
> +
> + TP_STRUCT__entry(
> + __field(u32, state)
> + __field(u32, cpu_id)
> + __cpumask(cpumask)
> + ),
> +
> + TP_fast_assign(
> + __entry->state = frequency;
> + __entry->cpu_id = cpu_id;
> + __assign_cpumask(cpumask, policy_cpus);
> + ),
> +
> + TP_printk("state=%lu cpu_id=%lu policy_cpus=%*pb",
> + (unsigned long)__entry->state,
> + (unsigned long)__entry->cpu_id,
> + cpumask_pr_args((struct cpumask *)__get_dynamic_array(cpumask)))
> );
>
> TRACE_EVENT(cpu_frequency_limits,
> diff --git a/kernel/trace/power-traces.c b/kernel/trace/power-traces.c
> index f2fe33573e54..a537e68a6878 100644
> --- a/kernel/trace/power-traces.c
> +++ b/kernel/trace/power-traces.c
> @@ -16,5 +16,5 @@
>
> EXPORT_TRACEPOINT_SYMBOL_GPL(suspend_resume);
> EXPORT_TRACEPOINT_SYMBOL_GPL(cpu_idle);
> -EXPORT_TRACEPOINT_SYMBOL_GPL(cpu_frequency);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(policy_frequency);
>
> diff --git a/samples/bpf/cpustat_kern.c b/samples/bpf/cpustat_kern.c
> index 7ec7143e2757..f485de0f89b2 100644
> --- a/samples/bpf/cpustat_kern.c
> +++ b/samples/bpf/cpustat_kern.c
> @@ -75,9 +75,9 @@ struct {
> } pstate_duration SEC(".maps");
>
> /*
> - * The trace events for cpu_idle and cpu_frequency are taken from:
> + * The trace events for cpu_idle and policy_frequency are taken from:
> * /sys/kernel/tracing/events/power/cpu_idle/format
> - * /sys/kernel/tracing/events/power/cpu_frequency/format
> + * /sys/kernel/tracing/events/power/policy_frequency/format
> *
> * These two events have same format, so define one common structure.
> */
> @@ -162,7 +162,7 @@ int bpf_prog1(struct cpu_args *ctx)
> */
> if (ctx->state != (u32)-1) {
>
> - /* record pstate after have first cpu_frequency event */
> + /* record pstate after have first policy_frequency event */
> if (!*pts)
> return 0;
>
> @@ -208,7 +208,7 @@ int bpf_prog1(struct cpu_args *ctx)
> return 0;
> }
>
> -SEC("tracepoint/power/cpu_frequency")
> +SEC("tracepoint/power/policy_frequency")
> int bpf_prog2(struct cpu_args *ctx)
> {
> u64 *pts, *cstate, *pstate, cur_ts, delta;
> diff --git a/samples/bpf/cpustat_user.c b/samples/bpf/cpustat_user.c
> index 356f756cba0d..f7e81f702358 100644
> --- a/samples/bpf/cpustat_user.c
> +++ b/samples/bpf/cpustat_user.c
> @@ -143,12 +143,12 @@ static int cpu_stat_inject_cpu_idle_event(void)
>
> /*
> * It's possible to have no any frequency change for long time and cannot
> - * get ftrace event 'trace_cpu_frequency' for long period, this introduces
> + * get ftrace event 'trace_policy_frequency' for long period, this introduces
> * big deviation for pstate statistics.
> *
> * To solve this issue, below code forces to set 'scaling_max_freq' to 208MHz
> - * for triggering ftrace event 'trace_cpu_frequency' and then recovery back to
> - * the maximum frequency value 1.2GHz.
> + * for triggering ftrace event 'trace_policy_frequency' and then recovery back
> + * to the maximum frequency value 1.2GHz.
> */
> static int cpu_stat_inject_cpu_frequency_event(void)
> {
> diff --git a/tools/perf/builtin-timechart.c b/tools/perf/builtin-timechart.c
> index 22050c640dfa..3ef1a2fd0493 100644
> --- a/tools/perf/builtin-timechart.c
> +++ b/tools/perf/builtin-timechart.c
> @@ -612,10 +612,10 @@ process_sample_cpu_idle(struct timechart *tchart __maybe_unused,
> }
>
> static int
> -process_sample_cpu_frequency(struct timechart *tchart,
> - struct evsel *evsel,
> - struct perf_sample *sample,
> - const char *backtrace __maybe_unused)
> +process_sample_policy_frequency(struct timechart *tchart,
> + struct evsel *evsel,
> + struct perf_sample *sample,
> + const char *backtrace __maybe_unused)
> {
> u32 state = evsel__intval(evsel, sample, "state");
> u32 cpu_id = evsel__intval(evsel, sample, "cpu_id");
> @@ -1541,7 +1541,7 @@ static int __cmd_timechart(struct timechart *tchart, const char *output_name)
> {
> const struct evsel_str_handler power_tracepoints[] = {
> { "power:cpu_idle", process_sample_cpu_idle },
> - { "power:cpu_frequency", process_sample_cpu_frequency },
> + { "power:policy_frequency", process_sample_policy_frequency },
> { "sched:sched_wakeup", process_sample_sched_wakeup },
> { "sched:sched_switch", process_sample_sched_switch },
> #ifdef SUPPORT_OLD_POWER_EVENTS
> @@ -1804,7 +1804,7 @@ static int timechart__record(struct timechart *tchart, int argc, const char **ar
> unsigned int backtrace_args_no = ARRAY_SIZE(backtrace_args);
>
> const char * const power_args[] = {
> - "-e", "power:cpu_frequency",
> + "-e", "power:policy_frequency",
> "-e", "power:cpu_idle",
> };
> unsigned int power_args_nr = ARRAY_SIZE(power_args);
perf timechart seem to do per-CPU reporting though?
So this is broken by not emitting an event per-CPU? At least with a simple s/cpu_frequency/policy_frequency/
like here.
Similar for the bpf samples technically...
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