[RFC/RFT][PATCH v2 0/6] PM / QoS: Introduce latency tolerance device PM QoS type

From: Rafael J. Wysocki
Date: Thu Jan 23 2014 - 08:27:41 EST

On Friday, January 17, 2014 03:42:13 PM Rafael J. Wysocki wrote:
> Hi All,
> On some platforms hardware may switch to an energy-saving mode on the fly
> on the basis of certain utilization metrics used by it. That usually is
> desirable from the energy conservation standpoint, but it generally causes
> latencies to increase which may adversely affect some operations. For this
> reason, the platforms in question usually provide some interfaces for software
> to indicate its latency tolerance and possibly to prevent the energy-saving
> modes from being selected too aggressively.
> The following series of patches introduces a device PM QoS type allowing
> those interfaces to be used by kernel code and user space. It is designed
> in analogy with the existing resume latency device PM QoS type, which allows
> some pieces of the existing device PM QoS code to be re-used and makes the
> new user space interface fit into the existing framework.
> Patch [1/5] modifies the names of symbols, variables, functions and structure
> fields associated with the existing resume latency device PM QoS type to
> avoid any confusion with the new one introduced by the subsequent patches.
> Patch [2/5] introduces a new field in struct pm_qos_constraints for specifying
> a special value to be returned as the effective requirement when the given list
> of PM QoS requirements is empty. That field is necessary for the new latency
> tolerance device PM QoS type.
> Patch [3/5] introduces the latency tolerance device PM QoS type along with
> documentation.
> Patch [4/5] modifies the ACPI LPSS (Low-Power Subsystem) driver to hook up
> LPSS devices to the new latency tolerance device PM QoS interface.
> Patch [5/5] modifies the dev_pm_qos_add_ancestor_request() routine so that it
> can be used by drivers of devices without hardware latency tolerance support
> for specifying their requirements via the ancestors of those devies.

As usual, testing uncovered some issues, so an updated series follows.


I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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