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author | Trond Myklebust <Trond.Myklebust@netapp.com> | 2008-03-19 17:59:44 -0400 |
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committer | Trond Myklebust <Trond.Myklebust@netapp.com> | 2008-03-19 17:59:44 -0400 |
commit | c7c350e92aab1bba68f26a6027b734adcf9824ba (patch) | |
tree | aa99bd94c3049dd871d9c030d70a5f3d87591a95 /Documentation/power/pm_qos_interface.txt | |
parent | 2f42b5d043ee271d1e5d30ecd77186b6c4d4e534 (diff) | |
parent | f8512ad0da16cbe156f3a7627971cdf0b39c4138 (diff) | |
download | linux-c7c350e92aab1bba68f26a6027b734adcf9824ba.tar.bz2 |
Merge branch 'hotfixes' into devel
Diffstat (limited to 'Documentation/power/pm_qos_interface.txt')
-rw-r--r-- | Documentation/power/pm_qos_interface.txt | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt new file mode 100644 index 000000000000..49adb1a33514 --- /dev/null +++ b/Documentation/power/pm_qos_interface.txt @@ -0,0 +1,59 @@ +PM quality of Service interface. + +This interface provides a kernel and user mode interface for registering +performance expectations by drivers, subsystems and user space applications on +one of the parameters. + +Currently we have {cpu_dma_latency, network_latency, network_throughput} as the +initial set of pm_qos parameters. + +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 requirements is maintained along with +an aggregated target value. The aggregated target value is updated with +changes to the requirement list or elements of the list. Typically the +aggregated target value is simply the max or min of the requirement values held +in the parameter list elements. + +From kernel mode the use of this interface is simple: +pm_qos_add_requirement(param_id, name, target_value): +Will insert a named element in the list for that identified PM_QOS parameter +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. + +pm_qos_update_requirement(param_id, name, new_target_value): +Will search the list identified by the param_id for the named list element and +then update its target value, calling the notification tree if the aggregated +target is changed. with that name is already registered. + +pm_qos_remove_requirement(param_id, name): +Will search the identified list for the named element and remove it, after +removal it will update the aggregate target and call the notification tree if +the target was changed as a result of removing the named requirement. + + +From user mode: +Only processes can register a pm_qos requirement. To provide for automatic +cleanup for process the interface requires the process to register its +parameter requirements in the following way: + +To register the default pm_qos target for the specific parameter, the process +must open one of /dev/[cpu_dma_latency, network_latency, network_throughput] + +As long as the device node is held open that process has a registered +requirement on the parameter. The name of the requirement is "process_<PID>" +derived from the current->pid from within the open system call. + +To change the requested target value the process needs to write a s32 value to +the open device node. This translates to a pm_qos_update_requirement call. + +To remove the user mode request for a target value simply close the device +node. + + + |