one of the parameters.
Two different PM QoS frameworks are available:
-1. PM QoS classes for cpu_dma_latency
-2. The per-device PM QoS framework provides the API to manage the
+ * CPU latency QoS.
+ * The per-device PM QoS framework provides the API to manage the
per-device latency constraints and PM QoS flags.
-Each parameters have defined units:
-
- * latency: usec
- * timeout: usec
- * throughput: kbs (kilo bit / sec)
- * memory bandwidth: mbs (mega bit / sec)
+The latency unit used in the PM QoS framework is the microsecond (usec).
1. PM QoS framework
===================
-The infrastructure exposes multiple misc device nodes one per implemented
-parameter. The set of parameters implement is defined by pm_qos_power_init()
-and pm_qos_params.h. This is done because having the available parameters
-being runtime configurable or changeable from a driver was seen as too easy to
-abuse.
-
-For each parameter a list of performance requests is maintained along with
-an aggregated target value. The aggregated target value is updated with
-changes to the request list or elements of the list. Typically the
-aggregated target value is simply the max or min of the request values held
-in the parameter list elements.
+A global list of CPU latency QoS requests is maintained along with an aggregated
+(effective) target value. The aggregated target value is updated with changes
+to the request list or elements of the list. For CPU latency QoS, the
+aggregated target value is simply the min of the request values held in the list
+elements.
+
Note: the aggregated target value is implemented as an atomic variable so that
reading the aggregated value does not require any locking mechanism.
+From kernel space the use of this interface is simple:
-From kernel mode the use of this interface is simple:
-
-void pm_qos_add_request(handle, param_class, target_value):
- Will insert an element into the list for that identified PM QoS class with the
- target value. Upon change to this list the new target is recomputed and any
- registered notifiers are called only if the target value is now different.
- Clients of pm_qos need to save the returned handle for future use in other
- pm_qos API functions.
+void cpu_latency_qos_add_request(handle, target_value):
+ Will insert an element into the CPU latency QoS list with the target value.
+ Upon change to this list the new target is recomputed and any registered
+ notifiers are called only if the target value is now different.
+ Clients of PM QoS need to save the returned handle for future use in other
+ PM QoS API functions.
-void pm_qos_update_request(handle, new_target_value):
+void cpu_latency_qos_update_request(handle, new_target_value):
Will update the list element pointed to by the handle with the new target
value and recompute the new aggregated target, calling the notification tree
if the target is changed.
-void pm_qos_remove_request(handle):
+void cpu_latency_qos_remove_request(handle):
Will remove the element. After removal it will update the aggregate target
and call the notification tree if the target was changed as a result of
removing the request.
-int pm_qos_request(param_class):
- Returns the aggregated value for a given PM QoS class.
+int cpu_latency_qos_limit():
+ Returns the aggregated value for the CPU latency QoS.
+
+int cpu_latency_qos_request_active(handle):
+ Returns if the request is still active, i.e. it has not been removed from the
+ CPU latency QoS list.
-int pm_qos_request_active(handle):
- Returns if the request is still active, i.e. it has not been removed from a
- PM QoS class constraints list.
+int cpu_latency_qos_add_notifier(notifier):
+ Adds a notification callback function to the CPU latency QoS. The callback is
+ called when the aggregated value for the CPU latency QoS is changed.
-int pm_qos_add_notifier(param_class, notifier):
- Adds a notification callback function to the PM QoS class. The callback is
- called when the aggregated value for the PM QoS class is changed.
+int cpu_latency_qos_remove_notifier(notifier):
+ Removes the notification callback function from the CPU latency QoS.
-int pm_qos_remove_notifier(int param_class, notifier):
- Removes the notification callback function for the PM QoS class.
+From user space:
-From user mode:
+The infrastructure exposes one device node, /dev/cpu_dma_latency, for the CPU
+latency QoS.
-Only processes can register a pm_qos request. To provide for automatic
+Only processes can register a PM QoS request. To provide for automatic
cleanup of a process, the interface requires the process to register its
-parameter requests in the following way:
+parameter requests as follows.
-To register the default pm_qos target for the specific parameter, the process
-must open /dev/cpu_dma_latency
+To register the default PM QoS target for the CPU latency QoS, the process must
+open /dev/cpu_dma_latency.
As long as the device node is held open that process has a registered
request on the parameter.
-To change the requested target value the process needs to write an s32 value to
-the open device node. Alternatively the user mode program could write a hex
-string for the value using 10 char long format e.g. "0x12345678". This
-translates to a pm_qos_update_request call.
+To change the requested target value, the process needs to write an s32 value to
+the open device node. Alternatively, it can write a hex string for the value
+using the 10 char long format e.g. "0x12345678". This translates to a
+cpu_latency_qos_update_request() call.
To remove the user mode request for a target value simply close the device
node.
projects / platform / kernel / linux-rpi.git / blobdiff