Messages in this thread | | | Subject | Re: [RFC PATCH 3/4] cpufreq: Add Active Stats calls tracking frequency changes | From | Lukasz Luba <> | Date | Tue, 22 Jun 2021 16:02:54 +0100 |
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On 6/22/21 3:51 PM, Rafael J. Wysocki 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?
True, it will get enough data after a first freq switch made by cpufreq governor. I don't want to race with schedutil and check the current freq, but I will check that option too.
> >> 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.
I see your point. Fair enough.
> > 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. >
Sure thing. I'll improve this.
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