On Thu, 2025-12-04 at 15:57 +0100, Rafael J. Wysocki wrote: > On Thu, Dec 4, 2025 at 1:49 PM Christian Loehle > <[email protected]> wrote: > > > > 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 <[email protected]> > > > --- > > > 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... > > This kind of boils down to whether or not tracepoints can be regarded > as ABI and to what extent. >
We have tools using tracing. We may need to check those tools. https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/tools/power/x86/intel_pstate_tracer/intel_pstate_tracer.py?h=next-20251204 https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/tools/power/x86/amd_pstate_tracer/amd_pstate_trace.py?h=next-20251204 Thanks, Srinivas > In this particular case, I'm not sure I agree with the stated > motivation. > > First of all, on systems with one CPU per cpufreq policy (the vast > majority of x86, including AMD, and the ARM systems using the CPPC > driver AFAICS), the "issue" at hand is actually a non-issue and > changing the name of the tracepoint alone would confuse things in > user > space IIUC. Those need to work the way they do today. > > On systems with multiple CPUs per cpufreq policy there is some extra > overhead related to the cpu_frequency tracepoint, but the if someone > is only interested in the "policy" frequency, they can filter out all > CPUs belonging to the same policy except for one from the traces, > don't they?
