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

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Date:   Mon, 15 Nov 2021 15:57:21 -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 11/9/21 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.

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
> 

--