Re: [PATCH v2 1/4] PM / EM: add devices to Energy Model
From: Lukasz Luba
Date: Fri Feb 07 2020 - 10:59:57 EST
Hi Quentin,
Thank you for the review, please find my comments below.
On 2/7/20 12:04 PM, Quentin Perret wrote:
On Thursday 06 Feb 2020 at 13:46:37 (+0000), lukasz.luba@xxxxxxx wrote:
2. Core APIs
@@ -70,14 +72,16 @@ CONFIG_ENERGY_MODEL must be enabled to use the EM framework.
Drivers are expected to register performance domains into the EM framework by
calling the following API::
- int em_register_perf_domain(cpumask_t *span, unsigned int nr_states,
- struct em_data_callback *cb);
+ int em_register_perf_domain(struct device *dev, unsigned int nr_states,
+ struct em_data_callback *cb, cpumask_t *cpus);
-Drivers must specify the CPUs of the performance domains using the cpumask
+Drivers must specify the device pointer of the performance domains as first
I find this sentence a little odd no?
Agree, this needs to be redefined.
argument, and provide a callback function returning <frequency, power> tuples
-for each capacity state. The callback function provided by the driver is free
+for each performance state. The callback function provided by the driver is free
to fetch data from any relevant location (DT, firmware, ...), and by any mean
-deemed necessary. See Section 3. for an example of driver implementing this
+deemed necessary. For other devices than CPUs the last argumant must be set to
s/argumant/argument
true
+NULL. Only for CPUfreq drivers it is obligatory to specify the cpumask.
Please note that as of today nothing mandates the caller to be a CPUFreq
driver -- it could be anything in theory. I'd say 'only for CPU devices'
instead.
Good point, I will change it into 'only for CPU devices'.
<snip>
@@ -24,51 +27,65 @@ struct em_cap_state {
/**
* em_perf_domain - Performance domain
- * @table: List of capacity states, in ascending order
- * @nr_cap_states: Number of capacity states
- * @cpus: Cpumask covering the CPUs of the domain
+ * @table: List of performance states, in ascending order
+ * @nr_perf_states: Number of performance states
+ * @priv: In case of EM for CPU device it is a Cpumask
+ * covering the CPUs of the domain
Could you turn @priv back into 'unsigned long priv[0];' and keep the
allocation as it is today ? That is, append the cpumask to the struct.
This empty pointer for non-CPU devices is just wasted space, and pointer
chasing isn't good for your caches. Given that you pre-allocate the pd
in em_create_pd() you could just have a special case for CPUs there I
suppose. And _is_cpu_em() will have to check the bus like you did in v1.
OK, I will change it to 'unsigned long priv[0];'. The argument of stall
because of missing cpumask when we probably already missed for 'em_pd'
in the scheduler code, is good for me.
*
- * A "performance domain" represents a group of CPUs whose performance is
- * scaled together. All CPUs of a performance domain must have the same
- * micro-architecture. Performance domains often have a 1-to-1 mapping with
- * CPUFreq policies.
+ * In case of CPU device, a "performance domain" represents a group of CPUs
+ * whose performance is scaled together. All CPUs of a performance domain
+ * must have the same micro-architecture. Performance domains often have
+ * a 1-to-1 mapping with CPUFreq policies.
+ * In case of other devices the 'priv' field is unused.
*/
struct em_perf_domain {
- struct em_cap_state *table;
- int nr_cap_states;
- unsigned long cpus[0];
+ struct em_perf_state *table;
+ int nr_perf_states;
+ void *priv;
};
<snip>
struct em_data_callback {
/**
- * active_power() - Provide power at the next capacity state of a CPU
- * @power : Active power at the capacity state in mW (modified)
- * @freq : Frequency at the capacity state in kHz (modified)
- * @cpu : CPU for which we do this operation
+ * active_power() - Provide power at the next performance state of a
+ * device
+ * @power : Active power at the performance state in mW (modified)
+ * @freq : Frequency at the performance state in kHz (modified)
+ * @dev : Device for which we do this operation (can be a CPU)
*
- * active_power() must find the lowest capacity state of 'cpu' above
+ * active_power() must find the lowest performance state of 'dev' above
* 'freq' and update 'power' and 'freq' to the matching active power
* and frequency.
*
- * The power is the one of a single CPU in the domain, expressed in
- * milli-watts. It is expected to fit in the [0, EM_CPU_MAX_POWER]
- * range.
+ * In case of CPUs, the power is the one of a single CPU in the domain,
+ * expressed in milli-watts. It is expected to fit in the
+ * [0, EM_MAX_POWER] range.
*
* Return 0 on success.
*/
- int (*active_power)(unsigned long *power, unsigned long *freq, int cpu);
+ int (*active_power)(unsigned long *power, unsigned long *freq,
+ struct device *dev);
Given that you've made explicit in the doc of struct em_perf_state that
'power' can be a 'total' value (static + dynamic), this could be renamed
I suppose.
I have check some literature and indeed 'active power' is not present,
but I could find 'active energy' and 'standby energy'. So we could
use 'active power' when we are talking in context of active energy.
In some other place I found 'Operating power (dynamic + leakage)' and
'Standby power' measurements for different architectures.
So I would prefer to keep 'active_power' which would mean the power
when a device was running (active).
<snip>
/**
* em_cpu_get() - Return the performance domain for a CPU
* @cpu : CPU to find the performance domain for
*
- * Return: the performance domain to which 'cpu' belongs, or NULL if it doesn't
+ * Returns the performance domain to which 'cpu' belongs, or NULL if it doesn't
* exist.
*/
struct em_perf_domain *em_cpu_get(int cpu)
{
- return READ_ONCE(per_cpu(em_data, cpu));
Since CPU perf domains are guaranteed to never go away, it'd be safe to
keep that per-CPU variable and avoid the locking and list manipulation
below. No strong opinion, though.
The functions em_cpu_get() and em_get_pd() are called only during
start phase (topology initialization or thermal setup). After that
these subsystems carry on with the returned pointer in their private
structures. So I would prefer to keep implementation clean and have all
EM structures in one list (avoiding the per-cpu).
+ struct em_device *em_dev;
+
+ mutex_lock(&em_pd_mutex);
+
+ if (list_empty(&em_pd_dev_list))
+ goto unlock;
+
+ list_for_each_entry(em_dev, &em_pd_dev_list, em_dev_list) {
+ if (!_is_cpu_em(em_dev->em_pd))
+ continue;
+
+ if (cpumask_test_cpu(cpu, em_span_cpus(em_dev->em_pd))) {
+ mutex_unlock(&em_pd_mutex);
+ return em_dev->em_pd;
+ }
+ }
+
+unlock:
+ mutex_unlock(&em_pd_mutex);
+ return NULL;
}
EXPORT_SYMBOL_GPL(em_cpu_get);
<snip>
/**
- * em_register_perf_domain() - Register the Energy Model of a performance domain
- * @span : Mask of CPUs in the performance domain
- * @nr_states : Number of capacity states to register
+ * em_register_perf_domain() - Register the Energy Model (EM) of a performance
+ * domain for the device
+ * @dev : Device for which the EM is to register
+ * @nr_states : Number of performance states to register
* @cb : Callback functions providing the data of the Energy Model
+ * @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
It should be policy->related_cpus actually (or 'real_cpus' even) -- PM_EM
ignores hotplug ATM. Perhaps we should document that somewhere ...
I also had this feeling until I have checked the cpufreq_online().
In that function after a call to driver's init function, the
'related_cpus' is set, not before (based on policy->cpus).
So I think it is safe to say 'policy->cpus' here.
https://elixir.bootlin.com/linux/latest/source/drivers/cpufreq/cpufreq.c#L1344
+ * type of devices this should be set to NULL.
*
* Create Energy Model tables for a performance domain using the callbacks
* defined in cb.
@@ -196,63 +361,129 @@ EXPORT_SYMBOL_GPL(em_cpu_get);
Thanks,
Quentin
Regards,
Lukasz