linux-kernel - RE: [Resend][PATCH V2] cpufreq: intel_pstate: allow trace in passive mode

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Date:   Fri, 5 Jan 2018 12:15:43 -0800
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Rafael J. Wysocki'" <rafael@...nel.org>,
        "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>
Cc:     "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        "'Linux Kernel Mailing List'" <linux-kernel@...r.kernel.org>,
        "'Linux PM'" <linux-pm@...r.kernel.org>,
        "Doug Smythies" <dsmythies@...us.net>
Subject: RE: [Resend][PATCH V2] cpufreq: intel_pstate: allow trace in passive mode

On 2017.12.18 16:25 Rafael J. Wysocki wrote:
> On 2017.12.18 15:31 Srinivas Pandruvada wrote:
>> On Fri, 2017-12-15 at 16:43 -0800, Doug Smythies wrote:
>>> Allow use of the trace_pstate_sample trace function
>>> when the intel_pstate driver is in passive mode.
>>> Since the core_busy and scaled_busy fields are not
>>> used, and it might be desirable to know which path
>>> through the driver was used, either intel_cpufreq_target
>>> or intel_cpufreq_fast_switch, re-task the core_busy
>>> field as a flag indicator.
>>>
>>> The user can then use the intel_pstate_tracer.py utility
>>> to summarize and plot the trace.
>>>
>>> In Passive mode the driver is only called if there is
>>> a need to change the target frequency, so durations
>>> (time gaps between calls) can be very very long. The user
>>> needs to understand, and not be confused by, this limitation.

The above statement isn't completely correct.
I changed it in V3.

>>>
>>> V2: prepare for resend. Rebase to current kernel, 4.15-rc3.
>>> Signed-off-by: Doug Smythies <dsmythies@...us.net>
>>> ---
>>>  drivers/cpufreq/intel_pstate.c | 50
>>> ++++++++++++++++++++++++++++++++++++++++--
>>>  1 file changed, 48 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/cpufreq/intel_pstate.c
>>> b/drivers/cpufreq/intel_pstate.c
>>> index 93a0e88..fe25d69 100644
>>> --- a/drivers/cpufreq/intel_pstate.c
>>> +++ b/drivers/cpufreq/intel_pstate.c
>>> @@ -1949,7 +1949,10 @@ static int intel_cpufreq_target(struct
>>> cpufreq_policy *policy,
>>>  {
>>>       struct cpudata *cpu = all_cpu_data[policy->cpu];
>>>       struct cpufreq_freqs freqs;
>>> -     int target_pstate;
>>> +     struct sample *sample;
>>> +     int target_pstate, from;
>>> +     u64 time;
>>> +     bool sample_taken;
>>>
>>>       update_turbo_state();
>>>
>>> @@ -1969,12 +1972,32 @@ static int intel_cpufreq_target(struct
>>> cpufreq_policy *policy,
>>>               break;
>>>       }
>>>       target_pstate = intel_pstate_prepare_request(cpu,
>>> target_pstate);
>>> +
>>> +     from = cpu->pstate.current_pstate;
>>> +     time = ktime_get();
>>> +     sample_taken = intel_pstate_sample(cpu, time);
>>> +
>> This is quite a bit of overhead for tracing.

Yes, it is a bit of added code, but without tracing abilities I
do not know how to investigate passive operation.

>> Why not fold the above two
>> statements in the next if () with conditional tracing?

No, I specifically want to do a trace sample, even if the target
is the same as last time. Why? Because we want to know the time
between calls to the driver, i.e. the duration. That information
is incredibly useful.

>>>       if (target_pstate != cpu->pstate.current_pstate) {
>>>               cpu->pstate.current_pstate = target_pstate;
>>>               wrmsrl_on_cpu(policy->cpu, MSR_IA32_PERF_CTL,
>>>                             pstate_funcs.get_val(cpu,
>>> target_pstate));
>>>       }
>>>       freqs.new = target_pstate * cpu->pstate.scaling;
>>> +
>>> +     if (sample_taken) {
>> if (trace_pstate_sample_enabled() && sample_taken) {
>>
>>> +             intel_pstate_calc_avg_perf(cpu);
>>> +             sample = &cpu->sample;
>>> +             trace_pstate_sample(0,
>> Not sure they are statement below are aligned correctly.

I'll double check in V3, thanks.
I suspect that somewhere along the way tabs got converted to spaces.

>>> +             0,
>>> +             from,
>>> +             cpu->pstate.current_pstate,
>>> +             sample->mperf,
>>> +             sample->aperf,
>>> +             sample->tsc,
>>> +             get_avg_frequency(cpu),
>>> +             fp_toint(cpu->iowait_boost * 100));
>>> +     }
>>> +
>> Same below in the intel_cpufreq_fast_switch().
>
> And it's quite a bit of code duplication too.
>
> Maybe put this into a separate function and call it from the two places?

O.K. yes, V3, coming shortly, has a separate function.

... Doug