Method and system for power management including device controller-based device use evaluation and power-state control

• US 20050125702A1
• Filed: 12/03/2003
• Published: 06/09/2005
• Est. Priority Date: 12/03/2003
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Huang, Hai, Keller, Thomas Walter Jr., Hensbergen, Eric Van
• Granted Patent: US 7,752,470 B2
• Time in Patent Office: Days
• US Class Current: 713/320
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3225 of memory devices
• CPC Class Codes: G06F 1/3275 Power saving in memory, e.g. RAM, cache
• CPC Class Codes: G06F 1/329 by task scheduling
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A method and system for power management including device controller-based device use evaluation and power-state control provides improved performance in a power-managed processing system. Per-device usage information is measured and evaluated during process execution and is retrieved from the device controller upon a context switch, so that upon reactivation of the process, the previous usage evaluation state can be restored. The device controller can then provide for per-process control of attached device power management states without intervention by the processor and without losing the historical evaluation state when a process is switched out. The device controller can control power-saving states of connected devices in conformity with the usage evaluation without processor intervention and across multiple process execution slices. The device controller may be a memory controller and the controlled devices memory modules or banks within modules if individual banks can be power-managed. Local thresholds provide the decision-making mechanism for each controlled device. The thresholds may be history-based, fixed or adaptive and are generally set initially by the operating system and may be updated by the memory controller adaptively or using historical collected usage evaluation counts or alternatively by the operating system via a system processor.

Claims

1. A device controller for coupling one or more controlled devices to one or more processors in a processing system, comprising:

a command unit for sending commands to said one or more devices;

at least one usage evaluator having an input coupled to an output of said command unit for evaluating a frequency of use of an associated controlled device; and

control logic coupled to said usage evaluator and further coupled to an input of said command unit for sending power management commands in response to said usage evaluator detecting is that a usage level of said associated device has fallen below a threshold level, whereby said device controller power manages said controlled device without intervention by said one or more processors.

2. The device controller of claim 1, further comprising:

an output port coupled to said at least one usage evaluator for reading a state of said at least one usage evaluator, whereby a state of said at least one usage evaluator may be stored external to said device controller; and

an input port coupled to said at least one usage evaluator for setting a state of said at least one usage evaluator, whereby said state of said at least one usage evaluator may be restored from information stored external to said device controller.

3. The device controller of claim 1, wherein said device controller is a memory controller, and wherein said controlled devices are memory modules.

4. The device controller of claim 3, wherein said at least one usage evaluator comprises an inter-arrival time counter for determining an interval between accesses to said associated memory module.

5. The device controller of claim 1, further comprising one or more power management control registers, each associated with a particular one of said one or more controlled devices, each coupled to an input port of said device controller and further coupled to said command unit, whereby a power management control state for said associated controlled device can be set by said one or more processors and set in said associated controlled device by said device controller.

6. The device controller of claim 5, wherein said power management control registers are further coupled to said at least one usage evaluator, whereby values of said power management control registers are adjusted in conformity with a result of said evaluating.

7. The device controller of claim 1, wherein said evaluator further comprises an adaptive threshold circuit for adjusting said threshold in response to said evaluated frequency of use of said one or more controlled devices.

8. The device controller of claim 1, wherein said one or more controlled devices include a counter for determining a level of usage of each controlled device during a current process, and wherein said device controller further comprises an input port coupled to each of said controlled devices for reading a value of said counter, and wherein said control logic updates said at associated evaluator in conformity with said value of said counter.

9. The device controller of claim 6, wherein said device controller is a memory controller, wherein said controlled devices are memory modules incorporating usage counters, and wherein said control logic is coupled to said command logic whereby said control logic periodically reads current counts from said memory modules.

10. A processing system, comprising:

a processor;

a memory coupled to said processor for storing program instructions and data values;

a device controller coupled to said processor;

one or more controlled devices coupled to said device controller, wherein said controlled devices have multiple power management states, and wherein said device controller includes a command unit for sending commands to said one or more devices, at least one usage evaluator having an input coupled to an output of said command unit for evaluating a frequency of use of an associated controlled device, and control logic coupled to said usage evaluator and further coupled to an input of said command unit for sending power management commands in response to said usage evaluator detecting that a usage level of said associated device has fallen below a threshold level, whereby said device controller power manages said controlled device without intervention by said processor.

11. The processing system of claim 10, wherein said device controller is a memory controller, and wherein said controlled devices are memory modules.

12. The processing system of claim 10, wherein said device controller further comprises:

an output port coupled to said at least one usage evaluator for reading a state of said at least one usage evaluator by said processor, whereby a state of said at least one usage evaluator may be stored in said memory by said processor; and

an input port coupled to said at least one usage evaluator for setting a state of said at least one usage evaluator by said processor, whereby said state of said at least one usage evaluator may be restored from said memory.

13. The processing system of claim 10, wherein said at least one usage evaluator comprises an inter-arrival time counter for determining an interval between commands sent to said associated controlled device.

14. The processing system of claim 10, wherein said device controller further comprises one or more power management control registers, each associated with a particular one of said one or more controlled devices, each coupled to an input port of said device controller and further coupled to said command unit, whereby a power management control state for said associated controlled device can be set by said processor and set in said associated controlled device by said device controller.

15. A method of managing power in a processing system, comprising:

sending power management setting information for devices controlled by a device controller to said device controller;

evaluating a usage of each of said controller devices within said device controller in order to determine whether or not said usage has fallen below a threshold; and

sending power management commands from said device controller to said controlled devices in conformity with a result of said determining, whereby said device controller manages a power management state of said controlled devices without processor intervention.

16. The method of claim 15, further comprising:

receiving an indication of a context switch activating a second process and deactivating a first process; and

in response to said receiving, saving a state of said evaluating, whereby said state may be restored at a subsequent context switch.

17. The method of claim 16, further comprising:

second receiving a second indication of a second context switch reactivating said first process;

in response to said second receiving, restoring said saved state of said evaluating, whereby said evaluating commences from the previously stored state.

18. The method of claim 15, further comprising retrieving usage counts from said controlled devices, and wherein said evaluating is performed in conformity with said retrieved usage counts.

19. The method of claim 15, further comprising adjusting said threshold in accordance with a result of said evaluating, whereby said evaluating is made adaptive to said usage.

20. The method of claim 15, wherein said device controller is a memory controller, wherein said controlled devices are memory modules, wherein said sending sends power management setting information to said memory modules, and wherein said evaluating determines a frequency of accesses to said memory modules.