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Richard Hughesbf1db692008-08-05 13:01:35 -07001PM Quality Of Service Interface.
Mark Grossd82b3512008-02-04 22:30:08 -08002
3This interface provides a kernel and user mode interface for registering
4performance expectations by drivers, subsystems and user space applications on
5one of the parameters.
6
7Currently we have {cpu_dma_latency, network_latency, network_throughput} as the
8initial set of pm_qos parameters.
9
Richard Hughesbf1db692008-08-05 13:01:35 -070010Each parameters have defined units:
11 * latency: usec
12 * timeout: usec
13 * throughput: kbs (kilo bit / sec)
14
Mark Grossd82b3512008-02-04 22:30:08 -080015The infrastructure exposes multiple misc device nodes one per implemented
16parameter. The set of parameters implement is defined by pm_qos_power_init()
17and pm_qos_params.h. This is done because having the available parameters
18being runtime configurable or changeable from a driver was seen as too easy to
19abuse.
20
21For each parameter a list of performance requirements is maintained along with
22an aggregated target value. The aggregated target value is updated with
23changes to the requirement list or elements of the list. Typically the
24aggregated target value is simply the max or min of the requirement values held
25in the parameter list elements.
26
27From kernel mode the use of this interface is simple:
28pm_qos_add_requirement(param_id, name, target_value):
29Will insert a named element in the list for that identified PM_QOS parameter
30with the target value. Upon change to this list the new target is recomputed
31and any registered notifiers are called only if the target value is now
32different.
33
34pm_qos_update_requirement(param_id, name, new_target_value):
35Will search the list identified by the param_id for the named list element and
36then update its target value, calling the notification tree if the aggregated
37target is changed. with that name is already registered.
38
39pm_qos_remove_requirement(param_id, name):
40Will search the identified list for the named element and remove it, after
41removal it will update the aggregate target and call the notification tree if
42the target was changed as a result of removing the named requirement.
43
44
45From user mode:
46Only processes can register a pm_qos requirement. To provide for automatic
47cleanup for process the interface requires the process to register its
48parameter requirements in the following way:
49
50To register the default pm_qos target for the specific parameter, the process
51must open one of /dev/[cpu_dma_latency, network_latency, network_throughput]
52
53As long as the device node is held open that process has a registered
54requirement on the parameter. The name of the requirement is "process_<PID>"
55derived from the current->pid from within the open system call.
56
57To change the requested target value the process needs to write a s32 value to
58the open device node. This translates to a pm_qos_update_requirement call.
59
60To remove the user mode request for a target value simply close the device
61node.
62
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64