linux-kernel - Re: [PATCH 1/2] PM: EM: Add min/max available performance state limits

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Message-ID: <ff527b90-416c-4fc0-8b03-b1e2968e71dd@arm.com>
Date: Mon, 22 Apr 2024 08:24:31 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: Hongyan Xia <hongyan.xia2@....com>
Cc: dietmar.eggemann@....com, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 sudeep.holla@....com, cristian.marussi@....com,
 linux-samsung-soc@...r.kernel.org, rafael@...nel.org,
 viresh.kumar@...aro.org, quic_sibis@...cinc.com
Subject: Re: [PATCH 1/2] PM: EM: Add min/max available performance state
 limits



On 4/9/24 15:47, Hongyan Xia wrote:
> On 03/04/2024 17:23, Lukasz Luba wrote:
>> [...]
>>
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index 927cc55ba0b3d..1a8b394251cb2 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -628,6 +628,8 @@ int em_dev_register_perf_domain(struct device 
>> *dev, unsigned int nr_states,
>>           goto unlock;
>>       dev->em_pd->flags |= flags;
>> +    dev->em_pd->min_ps = 0;
>> +    dev->em_pd->max_ps = nr_states - 1;
>>       em_cpufreq_update_efficiencies(dev, dev->em_pd->em_table->state);
>> @@ -856,3 +858,49 @@ int em_dev_update_chip_binning(struct device *dev)
>>       return em_recalc_and_update(dev, pd, em_table);
>>   }
>>   EXPORT_SYMBOL_GPL(em_dev_update_chip_binning);
>> +
>> +
>> +/**
>> + * em_update_performance_limits() - Update Energy Model with performance
>> + *                limits information.
>> + * @pd            : Performance Domain with EM that has to be updated.
>> + * @freq_min_khz    : New minimum allowed frequency for this device.
>> + * @freq_max_khz    : New maximum allowed frequency for this device.
>> + *
>> + * This function allows to update the EM with information about 
>> available
>> + * performance levels. It takes the minimum and maximum frequency in kHz
>> + * and does internal translation to performance levels.
>> + * Returns 0 on success or -EINVAL when failed.
>> + */
>> +int em_update_performance_limits(struct em_perf_domain *pd,
>> +        unsigned long freq_min_khz, unsigned long freq_max_khz)
>> +{
>> +    struct em_perf_state *table;
>> +    int min_ps = -1;
>> +    int max_ps = -1;
>> +    int i;
>> +
>> +    if (!pd)
>> +        return -EINVAL;
>> +
>> +    rcu_read_lock();
>> +    table = em_perf_state_from_pd(pd);
>> +
>> +    for (i = 0; i < pd->nr_perf_states; i++) {
>> +        if (freq_min_khz == table[i].frequency)
>> +            min_ps = i;
>> +        if (freq_max_khz == table[i].frequency)
>> +            max_ps = i;
>> +    }
>> +    rcu_read_unlock();
>> +
>> +    /* Only update when both are found and sane */
>> +    if (min_ps < 0 || max_ps < 0 || max_ps < min_ps)
>> +        return -EINVAL;
>> +
>> +    pd->min_ps = min_ps;
>> +    pd->max_ps = max_ps;
> 
> Are we sure we are protected against multiple simultaneous updates? Or 
> is this a concern for the caller?
> 
> The rest of the patch LGTM.
> 

I've tried to make it running fast for only one caller. Although,
if someone would like to use it from many places then locking should be
handled under in function (and I will use the existing mutex for it).

I'll change it. Thanks for the review.