Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 22 Jun 2021 15:51:58 +0200 | Subject | Re: [RFC PATCH 3/4] cpufreq: Add Active Stats calls tracking frequency changes |
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On Tue, Jun 22, 2021 at 3:42 PM Lukasz Luba <lukasz.luba@arm.com> wrote: > > > > On 6/22/21 1:28 PM, Rafael J. Wysocki wrote: > > On Tue, Jun 22, 2021 at 9:59 AM Lukasz Luba <lukasz.luba@arm.com> wrote: > >> > >> The Active Stats framework tracks and accounts the activity of the CPU > >> for each performance level. It accounts the real residency, when the CPU > >> was not idle, at a given performance level. This patch adds needed calls > >> which provide the CPU frequency transition events to the Active Stats > >> framework. > >> > >> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > >> --- > >> drivers/cpufreq/cpufreq.c | 5 +++++ > >> 1 file changed, 5 insertions(+) > >> > >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > >> index 802abc925b2a..d79cb9310572 100644 > >> --- a/drivers/cpufreq/cpufreq.c > >> +++ b/drivers/cpufreq/cpufreq.c > >> @@ -14,6 +14,7 @@ > >> > >> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > >> > >> +#include <linux/active_stats.h> > >> #include <linux/cpu.h> > >> #include <linux/cpufreq.h> > >> #include <linux/cpu_cooling.h> > >> @@ -387,6 +388,8 @@ static void cpufreq_notify_transition(struct cpufreq_policy *policy, > >> > >> cpufreq_stats_record_transition(policy, freqs->new); > >> policy->cur = freqs->new; > >> + > >> + active_stats_cpu_freq_change(policy->cpu, freqs->new); > >> } > >> } > >> > >> @@ -2085,6 +2088,8 @@ unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, > >> policy->cpuinfo.max_freq); > >> cpufreq_stats_record_transition(policy, freq); > >> > >> + active_stats_cpu_freq_fast_change(policy->cpu, freq); > >> + > > > > This is quite a bit of overhead and so why is it needed in addition to > > the code below? > > The code below is tracing, which is good for post-processing. We use in > our tool LISA, when we analyze the EAS decision, based on captured > trace data. > > This new code is present at run time, so subsystems like our thermal > governor IPA can use it and get better estimation about CPU used power > for any arbitrary period, e.g. 50ms, 100ms, 300ms, ...
So can it be made not run when the IPA is not using it?
> > > > And pretty much the same goes for the idle loop change. There is > > quite a bit of instrumentation in that code already and it avoids > > adding new locking for a reason. Why is it a good idea to add more > > locking to that code? > > This active_stats_cpu_freq_fast_change() doesn't use the locking, it > relies on schedutil lock in [1].
Ah, OK.
But it still adds overhead AFAICS.
> > > >> if (trace_cpu_frequency_enabled()) { > >> for_each_cpu(cpu, policy->cpus) > >> trace_cpu_frequency(freq, cpu); > >> -- > > > [1] > https://elixir.bootlin.com/linux/latest/source/kernel/sched/cpufreq_schedutil.c#L447
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