Abstract:
A method for automatically transitioning a processor to another performance level in a demand-based system. The invention provides for the automatic adjustment of processor frequency while preserving system responsiveness. The performance-level policy algorithm of the present invention detects increased processor utilization quickly enough that transition to a higher performance level is comparable to maximum system performance. The performance-level policy algorithm of an embodiment of the present invention delays processor transition to a lower performance level so that quick reversals in demand do not precipitate unnecessary transitioning.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to computer processor power management, and more specifically to an improved method for determining optimum performance level transition points.  
         BACKGROUND OF THE INVENTION  
         [0002]    Mobile PC manufacturers compete to increase system performance while reducing or at least maintaining power consumption. Mobile PC performance has increased dramatically. However, because it is not desirable to have larger batteries, and battery efficiency has not kept pace with processor performance, battery life for systems operating at peak performance has been drastically reduced. Manufacturers introduced the capability of power and performance control to prolong battery life. For example, a user watching a movie may wish to lower power consumption at the cost of diminished quality in order to prolong battery life long enough to complete the movie. Power and performance control is also used to control thermals. For example if a processor is overheating, the user may lower the performance thus lowering the power consumption and thus reducing the heat. In a typical power management system (PMS) the user provides a series of inputs to the power management portion of the operating system (OS). Alternatively, the PMS might be an embedded part of the OS. The user might input a preference toward battery life or toward system performance. The user might indicate energy conservation for DC operation and system performance optimization for AC operation.  
           [0003]    Historically, the reduction in power consumption had a linear relationship to the reduction in system performance. For example, a system running at 500 Mhz and using 10 watts could be throttled down to 250 Mhz and use 5 watts. When a system is run against a fixed workload, a PMS exhibiting this linear relationship provides little benefit in the way of prolonged battery life. That is, a system running at half the speed for twice as long will accomplish the same amount for the expended energy. The system will run cooler, but no more work is accomplished.  
           [0004]    More recent systems address this concern by taking advantage of the equation governing power consumption in CMOS circuits. This equation is P=kV 2 F, where P is the power consumed, k is some constant, V is the applied voltage and F is the operating frequency. Application of this equation shows that a small reduction in voltage may provide a large reduction in power consumption. Using a voltage-varying scheme in which the power is applied over time, therefore, allows for fixed workload to be accomplished with less energy and hence prolonged battery life. A typical PMS would provide a high-voltage/high-frequency mode for AC use and a low-voltage/low-frequency mode for DC use. The modes are implemented by a software program which detects whether the AC adapter has been plugged in, or not, and switches mode accordingly. The user could also provide input to the system and, if desired, chose not to switch to low performance mode. The PMS software may be incorporated within the OS and indicates to an application and driver that the power source has changed, the driver then communicates with the firmware that switches modes.  
           [0005]    Although such a PMS prolongs battery life, it does not address the issue of reduced performance. While on battery the system runs at a lower frequency and the user does not get the full benefit of system performance. If the user places the system into a high performance mode the battery life is diminished.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The present invention is illustrated by way of example and not intended to be limited by the figures of the accompanying drawings in which like references indicate similar elements and in which:  
         [0007]    [0007]FIG. 1 is a diagram illustrating a computing system for implementing the present invention;  
         [0008]    [0008]FIG. 2 is a block diagram of a power control circuit for implementing the present invention; and  
         [0009]    [0009]FIG. 3 depicts typical processor utilization graphs.  
     
    
     DETAILED DESCRIPTION  
       [0010]    An embodiment of the present invention provides a method for transition of processor performance levels in a demand-based system. A performance level is a specified operating frequency and its associated voltage. Automatic transition may use less transition overhead, thereby extending battery life. An embodiment of the invention provides for the automatic adjustment of processor frequency while preserving system responsiveness. In one embodiment of the invention the processor may be transitioned to multiple performance levels.  
         [0011]    [0011]FIG. 1 is a diagram illustrating an exemplary computer system  100  for implementing the present invention. The sampling of processor utilization, the detection of a change in processor utilization, and the transition of the processor to a different performance level, described herein, may be implemented and utilized within computing system  100 . Computing system  100  may represent a general-purpose computer, portable computer, or other like device. The components of computing system  100  are exemplary in which one or more components may be omitted or added.  
         [0012]    Referring to FIG. 1, computing system  100  includes a central processing unit  102  coupled to a display circuit  105 , main memory  104 , static memory  106 , and mass storage device  107  via bus  101 . Computing system  100  may also be coupled to a display  121 , keypad input  122 , cursor control  123 , hard copy device  124 , and input/output (I/O) devices  125  via bus  101 . Computing system  100  may contain frequency and voltage regulation circuitry as described below.  
         [0013]    Bus  101  is a standard system bus for communicating information and signals. Processor  102  is a processing unit for computing system  100 . Processor  102  may be used to process information for computing system  100 . Processor  102  includes a control unit  131 , an arithmetic logic unit (ALU)  132 , and several registers  133 , which are used to process information.  
         [0014]    Main memory  104  may be, e.g., a random access memory (RAM) or some other dynamic storage device, for storing information or instructions (program code), which are used by processor  102 . Main memory  104  may also store temporary variables or other intermediate information during execution of instructions by processor  102 . Static memory  106 , may be, e.g., a read only memory (ROM) and/or other static storage devices, for storing information or instructions, which may also be used by processor  102 . Mass storage device  107  may be, e.g., a hard or floppy disk drive or optical disk drive, for storing information or instructions for computing system  100 .  
         [0015]    Display  121  may be, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD). Display device  121  displays information or graphics to a user. Computing system  100  may interface with display  121  via display circuit  105 . Keypad input  122  is a alphanumeric input device for communicating information and command selections to computing system  100 . Cursor control  123  may be, e.g., a mouse, a trackball, or cursor direction keys, for controlling movement of an object on display  121 . Hard copy device  124  may be, e.g., a laser printer, for printing information on paper, film, or some other like medium. A number of input/output devices  125  may be coupled to computing system  100 .  
         [0016]    In one embodiment of the invention, processor  102  may also contain power management software  134  to allow user control of operating voltage and operating frequency. The power management software  134  may configure an I/O controller  150  to facilitate voltage and frequency scaling upon the occurrence of specified conditions. I/O controller  150  programs a register  136  within a clock generation circuit  135 . The programmed information indicates how the operating frequency of the clocking signal is to be altered. The clock generation circuit  135  monitors the register  136  and modifies the frequency of the clocking signals accordingly. After determining that the operating frequency has been reduced the I/O controller  150  generates a voltage modification control signal to a power supply circuit, not shown. The power supply circuit then reduces the voltage accordingly.  
         [0017]    The processor performance level transition policy algorithm, described herein, may be implemented by hardware and/or software contained within computing system  100 . For example, processor  102  may execute code or instructions stored in a machine-readable medium, e.g., main memory  104 , to decide when to transition the processor performance level on a processor that supports multiple performance levels.  
         [0018]    The machine-readable medium may include a mechanism that provides (i.e., stores and/or transmits) information in a form readable by a machine such as computer. For example, a machine-readable medium may include a read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices. The code or instructions may be represented by carrier wave signals, infrared signals, digital signals, and by other like signals.  
         [0019]    PMS may have several inputs into the software. The software may use these inputs to determine a performance level for the processor. Typically, the inputs include “power source”, high performance level for AC and low performance level for DC; “thermal”, an overriding environmental concern which will transition the processor to a lower (i.e., cooler) performance level if the processor overheats; and “user preference”, whereby a user may chose between conserving energy and increased performance. A demand-based PMS includes the input of “processor utilization” to allow for a transition to a higher performance level if the user has need of a higher level of performance. An embodiment of the present invention employs a fast up/slow down (FUSD) transition policy to monitor user demand upon the processor (i.e. processor utilization). An alternative embodiment may employ a slow up/fast down (SUFD) transition policy. The monitoring may be done by periodically reading the processor&#39;s Time Stamp Counter (TSC) and a high-resolution timer or utilizing existing native OS mechanisms. The TSC provides information about processor activity when the processor is not in a sleep state. The calculation of processor activity and frequency provides the utilization over a given period. Exemplary graphs of processor utilization for some typical workloads are shown in FIG. 2. FIG. 2 a  shows the processor utilization graph of, for example, a rendering. As shown the processor utilization rises quickly to near 100% and remains at a high level until the processing is complete. FIG. 2 b  shows the processor graph for a digital video disc (DVD). The processor utilization rises to a high level for extended periods and occasionally drops to significantly lower levels. FIG. 2 c  shows the processor graph for an idle system. As shown the processor utilization is at low level with the exception of spikes due to periodic OS housekeeping. An embodiment of the present invention will quickly detect a high processor utilization level and automatically switch the system to a high frequency performance level. When processor utilization drops off, the system is automatically switched to a low performance level. The ability to quickly transition between performance levels is not critical for a workload having a processor utilization graph as shown in FIGS. 2 a  and  2   c  . For workload such as that shown in FIG. 2 b  , however, quickly detecting changes in processor utilization and transitioning to an optimum performance level, may significantly improve energy efficiency.  
         [0020]    In accordance with the present invention, processor utilization is measured every T seconds. The processor-utilization monitoring period, T, should be small enough so that increased processor utilization is detected quickly, this maintains the responsiveness of the system. T should not be so small, however, as to overly tax the processor resources. When processor utilization is detected above a given threshold the system is automatically switched to a higher performance level. When processor utilization is detected below a given threshold the system is automatically switched to a lower performance level. Frequent switching between higher and lower performance levels taxes the processor, therefore the FUSD transition policy allows for less frequent switching from a high performance level to a lower one so that quick reversals in processor utilization will not result in frequent switching. For example, as shown in FIG. 2 b  the processor utilization reaches a switch-up threshold of, for example, 95% at time T 1 . The system automatically transitions to a higher performance level. At time T 2  the processor utilization drops below a switch-down threshold, for example 75%, but the system does not transition to a lower performance level. Instead, current performance level is maintained until processor utilization is monitored at time T 3 . At time T 3  the processor utilization is again above the switch-up threshold so the higher performance level is maintained. When, at time T 4 -T 6  the processor utilization level remains below the switch-down threshold for 3T seconds, the system is then transitioned to a lower performance level. The system remains at this lower performance level until the processor utilization once again rises above the switch-up threshold (i.e., until time T 9 ).  
         [0021]    [0021]FIG. 3 is a process flow diagram in accordance with one embodiment of the present invention. The process  300 , shown in FIG. 3 begins at operation  305  in which the processor utilization is calculated for the current performance level (i.e., at the current frequency). This calculation may be completed every T seconds. As described above, T is selected to be small enough to quickly detect an increase in processor utilization while not being so small as to unduly tax processor resources. Empirically, for one embodiment, a value of 150 milliseconds (ms) for T has been found to be adequate for typical systems with typical processor utilization graphs. At operation  310  the system determines if processor utilization is above a specified switch-up threshold. For one embodiment of the present invention the switch-up threshold is specified as 95% of the current performance level. If processor utilization is above the specified switch-up threshold, the system determines if processor utilization has been above this threshold longer than the switch-up period at operation  315 . The switch-up period may be equal to one or more processor-utilization monitoring periods T. For one embodiment the processor monitoring period is equal to 150 ms and the switch-up period is equal to 300 ms.  
         [0022]    If processor utilization has not been above the switch-up threshold longer than the switch-up period, the system waits until the next processor-utilization monitoring period, T, expires at operation  325  and returns to operation  305 . If processor utilization has been above the switch-up threshold longer than the switch-up period the system automatically transitions to the next higher performance level at operation  320  and then proceeds to operation  325  as described above.  
         [0023]    Referring again to operation  310 , if the system determines that processor utilization is not above the switch-up threshold, the system determines if processor utilization is below a specified switch-down threshold at operation  330 . For one embodiment of the present invention the switch-down threshold is specified as 95% of the next lower performance level. If processor utilization is below the specified switch-down threshold, the system determines if processor utilization has been below the switch-down threshold longer than the switch-down period at operation  335 . The switch-down period may be different than the switch-up period. For one embodiment the switch-up period is equal to 300 ms and the switch-down period is equal to 1000 ms. If processor utilization has not been below the switch-down threshold longer than the switch-down period, the system waits until the next processor-utilization monitoring period, T, expires at operation  325  and returns to operation  305 . If processor utilization has been below the switch-down threshold longer than the switch-down period the system automatically transitions to the next lower performance level at operation  340  and then proceeds to operation  325  as described above.  
         [0024]    Referring again to operation  330 , if the system determines that processor utilization is not below the switch-down threshold, the system waits until the next processor-utilization monitoring period, T, expires at operation  325  and returns to operation  305 .  
         [0025]    In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.  
       APPENDIX A  
       [0026]    William E. Alford, Reg. No. 37,764; Farzad E. Amini, Reg. No. 42,261; William Thomas Babbitt, Reg. No. 39,591; Carol F. Barry, Reg. No. 41,600; Jordan Michael Becker, Reg. No. 39,602; Lisa N. Benado, Reg. No. 39,995; Bradley J. Bereznak, Reg. No. 33,474; Michael A. Bernadicou, Reg. No. 35,934; Roger W. Blakely, Jr., Reg. No. 25,831; R. Alan Burnett, Reg. No. 46,149; Gregory D. Caldwell, Reg. No. 39,926; Andrew C. Chen, Reg. No. 43,544; Thomas M. Coester, Reg. No. 39,637; Donna Jo Coningsby, Reg. No. 41,684; Florin Corie, Reg. No. 46,244; Dennis M. deGuzman, Reg. No. 41,702; Stephen M. De Klerk, Reg. No. 46,503; Michael Anthony DeSanctis, Reg. No. 39,957; Daniel M. De Vos, Reg. No. 37,813; Sanjeet Dutta, Reg. No. 46,145; Matthew C. Fagan, Reg. No. 37,542; Tarek N. Fahmi, Reg. No. 41,402; George Fountain, Reg. No. 37,374; James Y. Go, Reg. No. 40,621; James A. Henry, Reg. No. 41,064; Libby N. Ho, Reg. No. 46,774; Willmore F. Holbrow III, Reg. No. 41,845; Sheryl Sue Holloway, Reg. No. 37,850; George W Hoover II, Reg. No. 32,992; Eric S. Hyman, Reg. No. 30,139; William W. Kidd, Reg. No. 31,772; Sang Hui Kim, Reg. No. 40,450; Walter T. Kim, Reg. No. 42,731; Eric T. King, Reg. No. 44,188; George Brian Leavell, Reg. No. 45,436; Kurt P. Leyendecker, Reg. No. 42,799; Gordon R. Lindeen III, Reg. No. 33,192; Jan Carol Little, Reg. No. 41,181; Robert G. Litts, Reg. No. 46,876; Joseph Lutz, Reg. No. 43,765; Michael J. Mallie, Reg. No. 36,591; Andre L. Marais, under 37 C.F.R. § 10.9(b); Paul A. Mendonsa, Reg. No. 42,879; Clive D. Menezes, Reg. No. 45,493; Chun M. Ng, Reg. No. 36,878; Thien T. Nguyen, Reg. No. 43,835; Thinh V. Nguyen, Reg. No. 42,034; Dennis A. Nicholls, Reg. No. 42,036; Robert B. O&#39;Rourke, Reg. No. 46,972; Daniel E. Ovanezian, Reg. No. 41,236; Kenneth B. Paley, Reg. No. 38,989; Gregg A. Peacock, Reg. No. 45,001; Marina Portnova, Reg. No. 45,750; William F. Ryann, Reg. 44,313; James H. Salter, Reg. No. 35,668; William W. Schaal, Reg. No. 39,018; James C. Scheller, Reg. No. 31,195; Jeffrey Sam Smith, Reg. No. 39,377; Maria McCormack Sobrino, Reg. No. 31,639; Stanley W. Sokoloff, Reg. No. 25,128; Judith A. Szepesi, Reg. No. 39,393; Vincent P. Tassinari, Reg. No. 42,179; Edwin H. Taylor, Reg. No. 25,129; John F. Travis, Reg. No. 43,203; Joseph A. Twarowski, Reg. No. 42,191; Tom Van Zandt, Reg. No. 43,219; Lester J. Vincent, Reg. No. 31,460; Glenn E. Von Tersch, Reg. No. 41,364; John Patrick Ward, Reg. No. 40,216; Mark L. Watson, Reg. No. 46,322; Thomas C. Webster, Reg. No. 46,154; and Norman Zafman, Reg. No. 26,250; my patent attorneys, and Firasat Ali, Reg. No. 45,715; Justin M. Dillon, Reg. No. 42,486; Thomas S. Ferrill, Reg. No. 42,532; and Raul Martinez, Reg. No. 46,904, my patent agents, of BLAKELY, SOKOLOFF, TAYLOR &amp; ZAFMAN LLP, with offices located at 12400 Wilshire Boulevard, 7th Floor, Los Angeles, Calif. 90025, telephone (310) 207-3800, and Alan K. Aldous, Reg. No. 31,905; Edward R. Brake, Reg. No. 37,784; Ben Burge, Reg. No. 42,372; Jeffrey S. Draeger, Reg. No. 41,000; Cynthia Thomas Faatz, Reg No. 39,973; John N. Greaves, Reg. No. 40,362; Seth Z. Kalson, Reg. No. 40,670; David J. Kaplan, Reg. No. 41,105; Peter Lam, Reg. No. 44,855; Charles A. Mirho, Reg. No. 41,199; Leo V. Novakoski, Reg. No. 37,198; Thomas C. Reynolds, Reg. No. 32,488; Kenneth M. Seddon, Reg. No. 43,105; Mark Seeley, Reg. No. 32,299; Steven P. Skabrat, Reg. No. 36,279; Howard A. Skaist, Reg. No. 36,008; Gene I. Su, Reg. No. 45,140; Calvin E. Wells, Reg. No. P43,256, Raymond J. Werner, Reg. No. 34,752; Robert G. Winkle, Reg. No. 37,474; Steven D. Yates, Reg. No. 42,242; and Charles K. Young, Reg. No. 39,435; my patent attorneys, of INTEL CORPORATION; and James R. Thein, Reg. No. 31,710, my patent attorney with full power of substitution and revocation, to prosecute this application and to transact all business in the Patent and Trademark Office connected herewith.  
       APPENDIX B  
     Title 37, Code of Federal Regulations, Section 1.56  Duty to Disclose Information Material to Patentability    
       [0027]    (a) A patent by its very nature is affected with a public interest. The public interest is best served, and the most effective patent examination occurs when, at the time an application is being examined, the Office is aware of and evaluates the teachings of all information material to patentability. Each individual associated with the filing and prosecution of a patent application has a duty of candor and good faith in dealing with the Office, which includes a duty to disclose to the Office all information known to that individual to be material to patentability as defined in this section. The duty to disclosure information exists with respect to each pending claim until the claim is cancelled or withdrawn from consideration, or the application becomes abandoned. Information material to the patentability of a claim that is cancelled or withdrawn from consideration need not be submitted if the information is not material to the patentability of any claim remaining under consideration in the application. There is no duty to submit information which is not material to the patentability of any existing claim. The duty to disclosure all information known to be material to patentability is deemed to be satisfied if all information known to be material to patentability of any claim issued in a patent was cited by the Office or submitted to the Office in the manner prescribed by §§ 1.97(b)-(d) and 1.98. However, no patent will be granted on an application in connection with which fraud on the Office was practiced or attempted or the duty of disclosure was violated through bad faith or intentional misconduct. The Office encourages applicants to carefully examine:  
         [0028]    (1) Prior art cited in search reports of a foreign patent office in a counterpart application, and  
         [0029]    (2) The closest information over which individuals associated with the filing or prosecution of a patent application believe any pending claim patentably defines, to make sure that any material information contained therein is disclosed to the Office.  
         [0030]    (b) Under this section, information is material to patentability when it is not cumulative to information already of record or being made or record in the application, and  
         [0031]    (1) It establishes, by itself or in combination with other information, a prima facie case of unpatentability of a claim; or  
         [0032]    (2) It refutes, or is inconsistent with, a position the applicant takes in:  
         [0033]    (i) Opposing an argument of unpatentability relied on by the Office, or  
         [0034]    (ii) Asserting an argument of patentability.  
         [0035]    A prima facie case of unpatentability is established when the information compels a conclusion that a claim is unpatentable under the preponderance of evidence, burden-of-proof standard, giving each term in the claim its broadest reasonable construction consistent with the specification, and before any consideration is given to evidence which may be submitted in an attempt to establish a contrary conclusion of patentability.  
         [0036]    (c) Individuals associated with the filing or prosecution of a patent application within the meaning of this section are:  
         [0037]    (1) Each inventor named in the application;  
         [0038]    (2) Each attorney or agent who prepares or prosecutes the application; and  
         [0039]    (3) Every other person who is substantively involved in the preparation or prosecution of the application and who is associated with the inventor, with the assignee or with anyone to whom there is an obligation to assign the application.  
         [0040]    (d) Individuals other than the attorney, agent or inventor may comply with this section by disclosing information to the attorney, agent, or inventor.