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authorTrond Myklebust <Trond.Myklebust@netapp.com>2008-03-19 17:59:44 -0400
committerTrond Myklebust <Trond.Myklebust@netapp.com>2008-03-19 17:59:44 -0400
commitc7c350e92aab1bba68f26a6027b734adcf9824ba (patch)
treeaa99bd94c3049dd871d9c030d70a5f3d87591a95 /Documentation/power/pm_qos_interface.txt
parent2f42b5d043ee271d1e5d30ecd77186b6c4d4e534 (diff)
parentf8512ad0da16cbe156f3a7627971cdf0b39c4138 (diff)
downloadlinux-c7c350e92aab1bba68f26a6027b734adcf9824ba.tar.bz2
Merge branch 'hotfixes' into devel
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+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.
+
+
+