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d82b3518 MG |
1 | PM quality of Service interface. |
2 | ||
3 | This interface provides a kernel and user mode interface for registering | |
4 | performance expectations by drivers, subsystems and user space applications on | |
5 | one of the parameters. | |
6 | ||
7 | Currently we have {cpu_dma_latency, network_latency, network_throughput} as the | |
8 | initial set of pm_qos parameters. | |
9 | ||
10 | The infrastructure exposes multiple misc device nodes one per implemented | |
11 | parameter. The set of parameters implement is defined by pm_qos_power_init() | |
12 | and pm_qos_params.h. This is done because having the available parameters | |
13 | being runtime configurable or changeable from a driver was seen as too easy to | |
14 | abuse. | |
15 | ||
16 | For each parameter a list of performance requirements is maintained along with | |
17 | an aggregated target value. The aggregated target value is updated with | |
18 | changes to the requirement list or elements of the list. Typically the | |
19 | aggregated target value is simply the max or min of the requirement values held | |
20 | in the parameter list elements. | |
21 | ||
22 | From kernel mode the use of this interface is simple: | |
23 | pm_qos_add_requirement(param_id, name, target_value): | |
24 | Will insert a named element in the list for that identified PM_QOS parameter | |
25 | with the target value. Upon change to this list the new target is recomputed | |
26 | and any registered notifiers are called only if the target value is now | |
27 | different. | |
28 | ||
29 | pm_qos_update_requirement(param_id, name, new_target_value): | |
30 | Will search the list identified by the param_id for the named list element and | |
31 | then update its target value, calling the notification tree if the aggregated | |
32 | target is changed. with that name is already registered. | |
33 | ||
34 | pm_qos_remove_requirement(param_id, name): | |
35 | Will search the identified list for the named element and remove it, after | |
36 | removal it will update the aggregate target and call the notification tree if | |
37 | the target was changed as a result of removing the named requirement. | |
38 | ||
39 | ||
40 | From user mode: | |
41 | Only processes can register a pm_qos requirement. To provide for automatic | |
42 | cleanup for process the interface requires the process to register its | |
43 | parameter requirements in the following way: | |
44 | ||
45 | To register the default pm_qos target for the specific parameter, the process | |
46 | must open one of /dev/[cpu_dma_latency, network_latency, network_throughput] | |
47 | ||
48 | As long as the device node is held open that process has a registered | |
49 | requirement on the parameter. The name of the requirement is "process_<PID>" | |
50 | derived from the current->pid from within the open system call. | |
51 | ||
52 | To change the requested target value the process needs to write a s32 value to | |
53 | the open device node. This translates to a pm_qos_update_requirement call. | |
54 | ||
55 | To remove the user mode request for a target value simply close the device | |
56 | node. | |
57 | ||
58 | ||
59 |