• Mark Gross's avatar
    pm qos infrastructure and interface · d82b3518
    Mark Gross authored
    The following patch is a generalization of the latency.c implementation done
    by Arjan last year.  It provides infrastructure for more than one parameter,
    and exposes a user mode interface for processes to register pm_qos
    expectations of processes.
    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
    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,
      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
      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
    [akpm@linux-foundation.org: fix warnings]
    [akpm@linux-foundation.org: fix build]
    [akpm@linux-foundation.org: fix build again]
    [akpm@linux-foundation.org: coding-style fixes]
    Signed-off-by: default avatarmark gross <mgross@linux.intel.com>
    Cc: "John W. Linville" <linville@tuxdriver.com>
    Cc: Len Brown <lenb@kernel.org>
    Cc: Jaroslav Kysela <perex@suse.cz>
    Cc: Takashi Iwai <tiwai@suse.de>
    Cc: Arjan van de Ven <arjan@infradead.org>
    Cc: Venki Pallipadi <venkatesh.pallipadi@intel.com>
    Cc: Adam Belay <abelay@novell.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
pm_qos_params.c 11.5 KB