Rafael,
2011/7/31 Rafael J. Wysocki <rjw@xxxxxxx>:
> On Thursday, July 28, 2011, jean.pihet@xxxxxxxxxxxxxx wrote:
>> From: Jean Pihet <j-pihet@xxxxxx>
>>
>> Re-design the PM QoS implementation to support the per-device
>> constraints:
>
> Well, I guess I should have reviewed this patch before [03/13].
Hmm indeed. The split of patches into API and implementation patches
wakes it rather confusing. I could add a comment in [03/13] about it.
...
>> - Misc fixes to improve code readability:
>> . rename of fields names (request, list, constraints, class),
>
> Please avoid doing renames along with functional changes. It makes reviewing
> extremely hard.
Ok I will move the renames in a different patch.
...
>> @@ -97,7 +97,12 @@ void device_pm_add(struct device *dev)
>> dev_name(dev->parent));
>> list_add_tail(&dev->power.entry, &dpm_list);
>> mutex_unlock(&dpm_list_mtx);
>> - plist_head_init(&dev->power.latency_constraints, &dev->power.lock);
>> + plist_head_init(&dev->power.latency_constraints.list, &dev->power.lock);
>> + dev->power.latency_constraints.target_value =
>> + PM_QOS_DEV_LAT_DEFAULT_VALUE;
>> + dev->power.latency_constraints.default_value =
>> + PM_QOS_DEV_LAT_DEFAULT_VALUE;
>> + dev->power.latency_constraints.type = PM_QOS_MIN;
>
> Perhaps add a helper doing these assignments?
This code is later moved into the device insertion and removal
functions. Cf. [05/13].
...
>> @@ -464,7 +465,7 @@ struct dev_pm_info {
>> unsigned long accounting_timestamp;
>> void *subsys_data; /* Owned by the subsystem. */
>> #endif
>> - struct plist_head latency_constraints;
>> + struct pm_qos_constraints latency_constraints;
>
> Why don't you simply call it "qos"? The data type provides the information
> about what it's for now.
Ok
...
>> +struct pm_qos_constraints {
>> + struct plist_head list;
>> + /*
>> + * Do not change target_value to 64 bit in order to guarantee
>> + * accesses atomicity
>> + */
>
> The comment doesn't belong here. Please put it outside of the structure
> definition or after the field name (or both, in which case the "inline"
> one may be shorter, like "must not be 64-bit").
Ok
>
>> + s32 target_value;
>> + s32 default_value;
>> + enum pm_qos_type type;
>> +};
>> +
>> +/*
>> + * Struct that is pre-allocated by the caller.
>> + * The handle is kept for future use (update, removal)
>> + */
>> struct pm_qos_request {
>> - struct plist_node list;
>> + struct plist_node node;
>
> Please avoid doing such things along with functional changes.
Ok
...
>> +enum pm_qos_req_action {
>> + PM_QOS_ADD_REQ,
>> + PM_QOS_UPDATE_REQ,
>> + PM_QOS_REMOVE_REQ
>> };
>
> A comment describing the meaning of these would be helpful.
Ok
...
>> -static inline int pm_qos_get_value(struct pm_qos_object *o)
>> +static inline int pm_qos_get_value(struct pm_qos_constraints *c)
>
> I'd remove the "inline" if you're at it. It's only a hint if the kernel
> is not built with "always inline" and the compiler should do the inlining
> anyway if that's a better choice.
Ok
...
>> -static inline s32 pm_qos_read_value(struct pm_qos_object *o)
>> +/*
>> + * pm_qos_read_value atomically reads and returns target_value.
>
> We have a standard for writing kerneldoc comments, please follow it.
Ok
>
>> + * target_value is updated upon update of the constraints list, using
>> + * pm_qos_set_value.
>> + *
>> + * Note: The lockless read path depends on the CPU accessing
>> + * target_value atomically. Atomic access is only guaranteed on all CPU
>> + * types linux supports for 32 bit quantites
>
> You should say "data types" rather than "quantities" here.
Ok
>
>> + */
>> +static inline s32 pm_qos_read_value(struct pm_qos_constraints *c)
>> {
>> - return o->target_value;
>> + if (c)
>> + return c->target_value;
>> + else
>> + return 0;
>> }
>>
>> -static inline void pm_qos_set_value(struct pm_qos_object *o, s32 value)
>> +static inline void pm_qos_set_value(struct pm_qos_constraints *c, s32 value)
>> {
>> - o->target_value = value;
>> + c->target_value = value;
>> }
>
> Well, I'm not sure that this function is necessary at all. You might as well
> simply remove it as far as I'm concerned.
The idea is to provide an efficient and lockless way to get the
aggregated constraint class value. When the constraints a re changing
the new value is calculated and stored using pm_qos_get_value and
pm_qos_set_value. Then pm_qos_read_value is used to retrieve the
value. For example cpuidle calls pm_qos_request which uses
pm_qos_read_value to get the CPU/DMA minimum latency.
>
>> -static void update_target(struct pm_qos_object *o, struct plist_node *node,
>> - int del, int value)
>> +static void update_target(struct pm_qos_request *req,
>> + enum pm_qos_req_action action, int value)
>> {
>> unsigned long flags;
>> - int prev_value, curr_value;
>> + int prev_value, curr_value, new_value;
>> + struct pm_qos_object *o = pm_qos_array[req->class];
>> + struct pm_qos_constraints *c;
>> +
>> + switch (req->class) {
>> + case PM_QOS_DEV_LATENCY:
>> + if (!req->dev) {
>> + WARN(1, KERN_ERR "PM QoS API called with NULL dev\n");
>> + return;
>> + }
>> + c = &req->dev->power.latency_constraints;
>> + break;
>> + case PM_QOS_CPU_DMA_LATENCY:
>> + case PM_QOS_NETWORK_LATENCY:
>> + case PM_QOS_NETWORK_THROUGHPUT:
>> + c = o->constraints;
>> + break;
>> + case PM_QOS_RESERVED:
>> + default:
>> + WARN(1, KERN_ERR "PM QoS API called with wrong class %d, "
>> + "req 0x%p\n", req->class, req);
>> + return;
>> + }
>
> Do we _really_ need that switch()?
>
> What about introducing dev_pm_qos_add_request() and friends specifically
> for devices, such that they will take the target device object (dev) as
> their first argument? Then, you could keep pm_qos_add_request() pretty
> much as is, right?
Yes but in that case I need to duplicate the API functions for devices
(add, update, remove). Those functions will call update_target.
I prefer the way this patch does it: simplify the API functions and
have only 1 place with the constraints management and notification
logic (in update_target).
>
>>
>> spin_lock_irqsave(&pm_qos_lock, flags);
>> - prev_value = pm_qos_get_value(o);
>> - /* PM_QOS_DEFAULT_VALUE is a signal that the value is unchanged */
>> - if (value != PM_QOS_DEFAULT_VALUE) {
>> +
>> + prev_value = pm_qos_get_value(c);
>> + if (value == PM_QOS_DEFAULT_VALUE)
>> + new_value = c->default_value;
>> + else
>> + new_value = value;
>
> What about writing that as
>
> new_value = value != PM_QOS_DEFAULT_VALUE ? value : c->default_value;
This is shorter but more difficult to read ;8
>
>> +
>> + switch (action) {
>> + case PM_QOS_REMOVE_REQ:
>> + plist_del(&req->node, &c->list);
>> + break;
>> + case PM_QOS_UPDATE_REQ:
>> /*
>> * to change the list, we atomically remove, reinit
>> * with new value and add, then see if the extremal
>> * changed
>> */
>> - plist_del(node, &o->requests);
>> - plist_node_init(node, value);
>> - plist_add(node, &o->requests);
>> - } else if (del) {
>> - plist_del(node, &o->requests);
>> - } else {
>> - plist_add(node, &o->requests);
>> + plist_del(&req->node, &c->list);
>> + case PM_QOS_ADD_REQ:
>> + plist_node_init(&req->node, new_value);
>> + plist_add(&req->node, &c->list);
>> + break;
>> + default:
>> + /* no action */
>> + ;
>> }
>> - curr_value = pm_qos_get_value(o);
>> - pm_qos_set_value(o, curr_value);
>> +
>> + curr_value = pm_qos_get_value(c);
>> + pm_qos_set_value(c, curr_value);
>> spin_unlock_irqrestore(&pm_qos_lock, flags);
>>
>> if (prev_value != curr_value)
>> blocking_notifier_call_chain(o->notifiers,
>
> That's why I'm thinking that it would be helpful to have a pointer
> to the notifier list from struct pm_qos_constraints .
I think having a per-device notifier list is complicating things. If a
subsystem needs te be notified it needs to register a notifier
callback for _every_ device in the system.
As a first implementation for OMAP the low-level PM code is using a
single notifier to retrieve all the devices latency constraints and
apply them to the pwer domains. I do not see how this could work with
a per-device notifier list.
>
> Besides, you can use "pm_qos_array[req->class]->notifiers" instead of
> "o->notifiers".
Ok
...
>> +static int find_pm_qos_object_by_minor(int minor)
>> +{
>> + int pm_qos_class;
>> +
>> + for (pm_qos_class = 0;
>> + pm_qos_class < PM_QOS_NUM_CLASSES; pm_qos_class++) {
>> + if (minor ==
>> + pm_qos_array[pm_qos_class]->pm_qos_power_miscdev.minor)
>> + return pm_qos_class;
>> + }
>> + return -1;
>> +}
>
> This function doesn't seem to be used anywhere, what's the purpose of it?
It is used by pm_qos_power_open in order to retrieve the class
associated with the MISC device.
BTW this patch is moving the code so that all the MISC related
functions are grouped together.
>
>> +
>> static int pm_qos_power_open(struct inode *inode, struct file *filp)
>> {
>> struct pm_qos_parameters pm_qos_params;
...
>
> Thanks,
> Rafael
Thanks,
Jean
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