Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 22 Jun 2021 16:59:09 +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 4:51 PM Rafael J. Wysocki <rafael@kernel.org> wrote: > > On Tue, Jun 22, 2021 at 4:09 PM Lukasz Luba <lukasz.luba@arm.com> wrote: > > > > > > > > On 6/22/21 2:51 PM, Rafael J. Wysocki wrote: > > > 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? > > > > I can make a Kconfig for IPA to select this ACTIVE_STATS. > > Also, I can add description that this framework is mostly needed > > for IPA, so don't enable it if you don't use IPA (default is 'n' > > so it shouldn't harm others). > > > > This Active Stats shouldn't be stopped when thermal zone is switching > > between governors at run time, e.g. IPA -> step_wise -> IPA > > because when IPA is set next time, it might not have correct CPU > > stats (what is the current frequency and for how long it has been > > actively used). > > But after a while it will collect enough useful data I suppose? > > > Beside, switching governors at run time is not a good idea > > (apart from stress testing them ;) ). > > > > > > > >>> > > >>> 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. > > > > Agree, it's an extra code. For platforms which use IPA it's a > > justifiable cost, weighted by better estimation thanks to this calls. > > For other platforms, this framework will be set to default 'n' option. > > A general problem with build-time configuration is for distros that > want to ship one kernel binary to run on multiple hardware platforms. > They need to enable those options anyway and then get the full cost on > the platforms that don't need it, but want to use the common binary > kernel. > > Again, please consider making this new code run only when it is needed > even if configured in and if it runs, make it as low-overhead as > possible.
Also, why don't you add these hooks to the drivers that are generally worked with by the IPA?
That you won't need to worry about the possible impact on everybody else.
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