Re: [PATCH v3 1/4] PM / EM: Add a flag indicating units of power values in Energy Model

[Lukasz Luba <lukasz.luba@arm.com>]

On 10/20/20 1:17 AM, Doug Anderson wrote:
> Hi,
> 
> On Mon, Oct 19, 2020 at 7:06 AM Lukasz Luba <lukasz.luba@arm.com> wrote:
>>
>> There are different platforms and devices which might use different scale
>> for the power values. Kernel sub-systems might need to check if all
>> Energy Model (EM) devices are using the same scale. Address that issue and
>> store the information inside EM for each device. Thanks to that they can
>> be easily compared and proper action triggered.
>>
>> Suggested-by: Daniel Lezcano <daniel.lezcano@linaro.org>
>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
>> ---
>>   drivers/cpufreq/scmi-cpufreq.c |  3 ++-
>>   drivers/opp/of.c               |  2 +-
>>   include/linux/energy_model.h   |  9 +++++++--
>>   kernel/power/energy_model.c    | 24 +++++++++++++++++++++++-
>>   4 files changed, 33 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
>> index e855e8612a67..3714a4cd07fa 100644
>> --- a/drivers/cpufreq/scmi-cpufreq.c
>> +++ b/drivers/cpufreq/scmi-cpufreq.c
>> @@ -188,7 +188,8 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>>          policy->fast_switch_possible =
>>                  handle->perf_ops->fast_switch_possible(handle, cpu_dev);
>>
>> -       em_dev_register_perf_domain(cpu_dev, nr_opp, &em_cb, policy->cpus);
>> +       em_dev_register_perf_domain(cpu_dev, nr_opp, &em_cb, policy->cpus,
>> +                                   false);
>>
>>          return 0;
>>
>> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
>> index 874b58756220..9e1307061de5 100644
>> --- a/drivers/opp/of.c
>> +++ b/drivers/opp/of.c
>> @@ -1333,7 +1333,7 @@ int dev_pm_opp_of_register_em(struct device *dev, struct cpumask *cpus)
>>                  goto failed;
>>          }
>>
>> -       ret = em_dev_register_perf_domain(dev, nr_opp, &em_cb, cpus);
>> +       ret = em_dev_register_perf_domain(dev, nr_opp, &em_cb, cpus, true);
>>          if (ret)
>>                  goto failed;
>>
>> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
>> index b67a51c574b9..2c31d79bb922 100644
>> --- a/include/linux/energy_model.h
>> +++ b/include/linux/energy_model.h
>> @@ -29,6 +29,8 @@ struct em_perf_state {
>>    * em_perf_domain - Performance domain
>>    * @table:             List of performance states, in ascending order
>>    * @nr_perf_states:    Number of performance states
>> + * @milliwatts:                Flag indicating the power values are in milli-Watts
>> + *                     or some other scale.
>>    * @cpus:              Cpumask covering the CPUs of the domain. It's here
>>    *                     for performance reasons to avoid potential cache
>>    *                     misses during energy calculations in the scheduler
>> @@ -43,6 +45,7 @@ struct em_perf_state {
>>   struct em_perf_domain {
>>          struct em_perf_state *table;
>>          int nr_perf_states;
>> +       bool milliwatts;
>>          unsigned long cpus[];
>>   };
>>
>> @@ -79,7 +82,8 @@ struct em_data_callback {
>>   struct em_perf_domain *em_cpu_get(int cpu);
>>   struct em_perf_domain *em_pd_get(struct device *dev);
>>   int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>> -                               struct em_data_callback *cb, cpumask_t *span);
>> +                               struct em_data_callback *cb, cpumask_t *spani,
>> +                               bool milliwatts);
>>   void em_dev_unregister_perf_domain(struct device *dev);
>>
>>   /**
>> @@ -186,7 +190,8 @@ struct em_data_callback {};
>>
>>   static inline
>>   int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>> -                               struct em_data_callback *cb, cpumask_t *span)
>> +                               struct em_data_callback *cb, cpumask_t *span,
>> +                               bool milliwatts)
>>   {
>>          return -EINVAL;
>>   }
>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
>> index c1ff7fa030ab..efe2a595988e 100644
>> --- a/kernel/power/energy_model.c
>> +++ b/kernel/power/energy_model.c
>> @@ -52,6 +52,17 @@ static int em_debug_cpus_show(struct seq_file *s, void *unused)
>>   }
>>   DEFINE_SHOW_ATTRIBUTE(em_debug_cpus);
>>
>> +static int em_debug_units_show(struct seq_file *s, void *unused)
>> +{
>> +       struct em_perf_domain *pd = s->private;
>> +       char *units = pd->milliwatts ? "milliWatts" : "bogoWatts";
>> +
>> +       seq_printf(s, "%s\n", units);
>> +
>> +       return 0;
>> +}
>> +DEFINE_SHOW_ATTRIBUTE(em_debug_units);
>> +
>>   static void em_debug_create_pd(struct device *dev)
>>   {
>>          struct dentry *d;
>> @@ -64,6 +75,8 @@ static void em_debug_create_pd(struct device *dev)
>>                  debugfs_create_file("cpus", 0444, d, dev->em_pd->cpus,
>>                                      &em_debug_cpus_fops);
>>
>> +       debugfs_create_file("units", 0444, d, dev->em_pd, &em_debug_units_fops);
>> +
>>          /* Create a sub-directory for each performance state */
>>          for (i = 0; i < dev->em_pd->nr_perf_states; i++)
>>                  em_debug_create_ps(&dev->em_pd->table[i], d);
>> @@ -250,17 +263,24 @@ EXPORT_SYMBOL_GPL(em_cpu_get);
>>    * @cpus       : Pointer to cpumask_t, which in case of a CPU device is
>>    *             obligatory. It can be taken from i.e. 'policy->cpus'. For other
>>    *             type of devices this should be set to NULL.
>> + * @milliwatts : Flag indicating that the power values are in milliWatts or
>> + *             in some other scale. It must be set properly.
>>    *
>>    * Create Energy Model tables for a performance domain using the callbacks
>>    * defined in cb.
>>    *
>> + * The @milliwatts is important to set with correct value. Some kernel
>> + * sub-systems might rely on this flag and check if all devices in the EM are
>> + * using the same scale.
>> + *
>>    * If multiple clients register the same performance domain, all but the first
>>    * registration will be ignored.
> 
> Should the bullet point above be changed?
> 
> I haven't dug through all the code so I may be being naive, but it
> seems like if someone registers with "milliWatts" set to true then it
> should ignore the old values where milliWatts were false?  Otherwise,
> I think, if SCMI registers some numbers first does that mean we can't
> later register updated numbers in the device tree?  Also, what happens
> when some devices register with milliWatts, some with bogoWatts, and
> some with both?  How do we decide what we should be using and what we
> should be throwing away?

When the SCMI is used, there is no DT involved. The SCMI provides
get_power() callback and protocol supports this. The values are coming
from FW. SCMI also requires that the scale is consistent across perf
domains, so no need to 'align' these devices to the same scale.

You cannot register EM twice for the same device, the existing code
already does not allow for that.
The EM internally does not track devices, the device struct has em_pd
field. It is up the the client framework or governor e.g. IPA to
check all power actors if some of them use abstract scale and other
milliWatts.

> 
> As per my response in the cover letter, I guess one option would be to
> try to figure out a bogoWatts to milliWatts conversion factor the
> first time someone tried to register once one way and once the other
> way?

It is not possible.

Regards,
Lukasz

> 
> 
> -Doug
>