linux-kernel - Re: [PATCH v4 4/5] cpufreq: qcom-cpufreq-hw: Use new thermal pressure update function

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Message-ID: <911760d9-b137-5c79-d072-c2f473a3cc6a@linaro.org>
Date:   Mon, 15 Nov 2021 18:39:18 -0500
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, steev@...i.org,
        sudeep.holla@....com, will@...nel.org, catalin.marinas@....com,
        linux@...linux.org.uk, gregkh@...uxfoundation.org,
        rafael@...nel.org, viresh.kumar@...aro.org, amitk@...nel.org,
        daniel.lezcano@...aro.org, amit.kachhap@...il.com,
        bjorn.andersson@...aro.org, agross@...nel.org
Subject: Re: [PATCH v4 4/5] cpufreq: qcom-cpufreq-hw: Use new thermal pressure
 update function



On 11/15/21 3:57 PM, Thara Gopinath wrote:
> 
> 
> On 11/9/21 2:57 PM, Lukasz Luba wrote:
>> Thermal pressure provides a new API, which allows to use CPU frequency
>> as an argument. That removes the need of local conversion to capacity.
>> Use this new API and remove old local conversion code.
>>
>> The new arch_update_thermal_pressure() also accepts boost frequencies,
>> which solves issue in the driver code with wrong reduced capacity
>> calculation. The reduced capacity was calculated wrongly due to
>> 'policy->cpuinfo.max_freq' used as a divider. The value present there was
>> actually the boost frequency. Thus, even a normal maximum frequency value
>> which corresponds to max CPU capacity (arch_scale_cpu_capacity(cpu_id))
>> is not able to remove the capping.

Also I failed to mention that, currently freq_factor is initialized as 
cpuinfo.max_freq / 1000 which means again all the issues you mentioned 
below can be hit, if some cpufreq driver decides to set boost at init.
I have sent a patch earlier today to fix this.

https://lore.kernel.org/linux-arm-msm/20211115201010.68567-1-thara.gopinath@linaro.org/T/#u

-- 
Warm Regards
Thara (She/Her/Hers)
> 
> Yes, although cpuinfo.max_freq does not reflect the boost frequency 
> unless boost is enabled atleast once. I have sent a patch to fix this. 
> But I agree that using cpuinfo.max_freq has issues you have mentioned in 
> this patch if boost is enabled once.
> 
> So, for this patch
> 
> Reviewed-by: Thara Gopinath <thara.gopinath@...aro.org>
> 
> Warm Regards
> Thara (She/Her/Hers)
>>
>> The second side effect which is solved is that the reduced frequency 
>> wasn't
>> properly translated into the right reduced capacity,
>> e.g.
>> boost frequency = 3000MHz (stored in policy->cpuinfo.max_freq)
>> max normal frequency = 2500MHz (which is 1024 capacity)
>> 2nd highest frequency = 2000MHz (which translates to 819 capacity)
>>
>> Then in a scenario when the 'throttled_freq' max allowed frequency was
>> 2000MHz the driver translated it into 682 capacity:
>> capacity = 1024 * 2000 / 3000 = 682
>> Then set the pressure value bigger than actually applied by the HW:
>> max_capacity - capacity => 1024 - 682 = 342 (<- thermal pressure)
>> Which was causing higher throttling and misleading task scheduler
>> about available CPU capacity.
>> A proper calculation in such case should be:
>> capacity = 1024 * 2000 / 2500 = 819
>> 1024 - 819 = 205 (<- thermal pressure)
>>
>> This patch relies on the new arch_update_thermal_pressure() handling
>> correctly such use case (with boost frequencies).
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
>>   drivers/cpufreq/qcom-cpufreq-hw.c | 15 +++------------
>>   1 file changed, 3 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c 
>> b/drivers/cpufreq/qcom-cpufreq-hw.c
>> index 0138b2ec406d..248135e5087e 100644
>> --- a/drivers/cpufreq/qcom-cpufreq-hw.c
>> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
>> @@ -275,10 +275,10 @@ static unsigned int 
>> qcom_lmh_get_throttle_freq(struct qcom_cpufreq_data *data)
>>   static void qcom_lmh_dcvs_notify(struct qcom_cpufreq_data *data)
>>   {
>> -    unsigned long max_capacity, capacity, freq_hz, throttled_freq;
>>       struct cpufreq_policy *policy = data->policy;
>>       int cpu = cpumask_first(policy->cpus);
>>       struct device *dev = get_cpu_device(cpu);
>> +    unsigned long freq_hz, throttled_freq;
>>       struct dev_pm_opp *opp;
>>       unsigned int freq;
>> @@ -295,17 +295,8 @@ static void qcom_lmh_dcvs_notify(struct 
>> qcom_cpufreq_data *data)
>>       throttled_freq = freq_hz / HZ_PER_KHZ;
>> -    /* Update thermal pressure */
>> -
>> -    max_capacity = arch_scale_cpu_capacity(cpu);
>> -    capacity = mult_frac(max_capacity, throttled_freq, 
>> policy->cpuinfo.max_freq);
>> -
>> -    /* Don't pass boost capacity to scheduler */
>> -    if (capacity > max_capacity)
>> -        capacity = max_capacity;
>> -
>> -    arch_set_thermal_pressure(policy->related_cpus,
>> -                  max_capacity - capacity);
>> +    /* Update thermal pressure (the boost frequencies are accepted) */
>> +    arch_update_thermal_pressure(policy->related_cpus, throttled_freq);
>>       /*
>>        * In the unlikely case policy is unregistered do not enable
>>
>