Patent Document

This patent application is a continuation of U.S. application Ser. No. 12/401,538, filed Mar. 10, 2009, now pending, which is a continuation of U.S. application Ser. No. 11/026,705, filed Dec. 30, 2004, now U.S. Pat. No. 7,502,948. Both of these earlier applications are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Technical Field 
     One or more embodiments of the present invention generally relate to operating point management. In particular, certain embodiments relate to managing operating points in multi-core processing architectures. 
     Discussion 
     The popularity of computing systems continues to grow and the demand for more complex processing architectures has experienced historical escalations. For example, multi-core processors are becoming more prevalent in the computing industry and are likely to be used in servers, desktop personal computers (PCs), notebook PCs, personal digital assistants (PDAs), wireless “smart” phones, and so on. As the number of processor cores in a system increases, the potential maximum power also increases. Increased power consumption translates into more heat, which poses a number of difficulties for computer designers and manufacturers. For example, device speed and long term reliability can deteriorate as temperature increases. If temperatures reach critically high levels, the heat can cause malfunction, degradations in lifetime or even permanent damage to parts. 
     While a number of cooling solutions have been developed, a gap continues to grow between the potential heat and the cooling capabilities of modern computing systems. In an effort to narrow this gap, some approaches to power management in computer processors involve the use of one or more on-die temperature sensors in conjunction with a power reduction mechanism. The power reduction mechanism is typically turned on and off (e.g., “throttled”) according to the corresponding temperature sensor&#39;s state in order to reduce power consumption. Other approaches involve alternatively switching between low and high frequency/voltage operating points. 
     While these solutions have been acceptable under certain circumstances, there remains considerable room for improvement. For example, these solutions tend to make the system performance more difficult to determine (i.e., the solutions tend to be “non-deterministic”). In fact, temperature based throttling is often highly dependent upon ambient conditions, which can lower the level of performance predictability. For example, on a warm day, more throttling (and therefore lower performance) is likely to occur than on a cool day for the same usage model. In addition, reducing power by throttling between operating points can add to the inconsistency of the user&#39;s experience. These drawbacks may be magnified when the gap between the dissipated power and the external cooling capabilities increases due to the presence of multiple processor cores in the system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various advantages of the embodiments of the present invention will become apparent to one skilled in the art by reading the following specification and appended claims, and by referencing the following drawings, in which: 
         FIG. 1  is a diagram of an example of a processing architecture according to one embodiment of the invention; 
         FIG. 2  is a diagram of an example of a system according to one embodiment of the invention; 
         FIG. 3  is a flowchart of an example of a method of managing operating points according to one embodiment of the invention; 
         FIG. 4  is a flowchart of an example of a process of determining a number of active cores according to one embodiment of the invention; and 
         FIG. 5  is a flowchart of an example of a process of selecting a maximum operating point according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present invention. It will be evident, however, to one skilled in the art that the embodiments of the present invention may be practiced without these specific details. In other instances, specific apparatus structures and methods have not been described so as not to obscure the embodiments of the present invention. The following description and drawings are illustrative of the embodiments of the invention and are not to be construed as limiting the embodiments of the invention. 
       FIG. 1  shows a processing architecture  10  having a plurality of processor cores  12  ( 12   a ,  12   b ), an activity module  14  and a plurality of maximum operating points  16  ( 16   a ,  16   b ) from which to select. The processor cores  12  can be similar to a Pentium® 4 processor core available from Intel® Corporation in Santa Clara, Calif., where each core  12  may be fully functional with instruction fetch units, instruction decoders, level one (L1) cache, execution units, and so on (not shown). In addition, the activity module  14  may be implemented in fixed functionality hardware such as complementary metal oxide semiconductor (CMOS) technology, in microcode, in software (e.g., as part of an operating system/OS), or any combination thereof. In the illustrated example, the activity module  14  is implemented in hardware. 
     In one example, each of the maximum operating points  16  includes a maximum operating frequency and voltage. The maximum operating points  16  can be determined based on knowledge of the cooling solutions available to the system and/or the thermal constraints of the system. For example, it may be determined that in a dual core architecture with only one core active, the system can be properly cooled if the active core is limited to a maximum operating frequency of 2.0 GHz (and/or a core voltage of 1.7 V). It may also be known, however, that if both cores are active, the cores should be limited to a maximum operating frequency of 1.5 GHz (and/or a core voltage of 1.35 V) in order for the cooling solution to be effective. The illustrated activity module  14  determines the number  18  of active cores in the plurality of processor cores  12  and selects a maximum operating point  17  for the active cores based on the number  18  of active cores. The maximum operating points  16  could be stored in a configuration table. 
     For example, the activity module  14  might make use of a configuration table such as the following Table I, to select a maximum operating point in a dual core architecture. 
                                 TABLE I                       # Active   Max Freq.                           1   2.0 GHz           2   1.5 GHz                        
Where the first maximum operating point  16   a  is assigned the value of 2.0 GHz and the second maximum operating point  16   b  is assigned the value of 1.5 GHz. Thus, if the activity module  14  determines that the first core  12   a  is active and the second core  12   b  is inactive, the number of active cores would be one and the first maximum operating point  16   a  (i.e., a maximum operating frequency of 2.0 GHz) would be selected for the first core  12   a . Similarly, if it is determined that the first core  12   a  is inactive and the second core  12   b  is active, the first maximum operating point  16   a  (i.e., a maximum operating frequency of 2.0 GHz) would be selected for the second core  12   b.  
 
     If, on the other hand, the activity module  14  determines that both the first core  12   a  and the second core  12   b  are active, the number of active cores would be two and the second maximum operating point  16   b  (i.e., a maximum operating frequency of 1.5 GHz) would be selected for both the first core  12   a  and the second core  12   b . Thus, under the above scenario, the illustrated activity module  14  could determine that both cores  12   a ,  12   b  are active and therefore set the second maximum operating point  16   b  as the selected maximum operating point  17 . Specific frequencies are given to facilitate discussion only. 
     By selecting the maximum operating point  17  based on the number  18  of active cores, the architecture  10  provides a number of advantages over conventional techniques. For example, the gap between the potential maximum power and the available cooling capabilities can be narrowed in a fashion that is not directly dependent upon temperature. Because the dependency on ambient temperature conditions can be minimized, more predictable performance can result. The approaches described herein are more deterministic than conventional approaches. In addition, limiting the operating point based on the number of active cores increases the effectiveness of the available cooling solutions. 
     The maximum operating point  17  may also be selected based on active core performance levels  19 , which can be determined by the activity module  14 . In particular, the processor cores  12  may be able to operate at different performance levels based on a variety of factors. For example, one approach may involve switching between low and high frequency/voltage operating points based on core utilization and/or temperature. In any case, it may be determined that an active core is running at a relatively low performance level, which may allow the other core(s) to operate at a higher performance level than would be permitted under a pure active/idle determination. 
     For example, it may be determined that cores  12   a  and  12   b  are active and that the first core  12   a  is operating at 1.0 GHz. It may also be determined that under such a condition, the second core  12   b  could operate at a frequency as high as 1.86 GHz without exceeding the cooling capability of the system. Rather than selecting the maximum operating point  17  for both cores to be 1.5 GHz, the activity module  14  could use the active core performance levels  19  to set a first core maximum operating point of 1.0 GHz and a second core maximum operating point of 1.86 GHz. Thus, the selected maximum operating point  17  could have a per-core component. 
     Turning now to  FIG. 2 , a system  20  having a multi-core processor  22  is shown, where the system  20  may be part of a server, desktop personal computer (PC), notebook PC, handheld computing device, etc. In the illustrated example, the processor  22  has an activity module  14 ′, a plurality of processor cores  12 ′ ( 12   a ′- 12   n ′) and a voltage and frequency controller  24 . 
     The illustrated system  20  also includes one or more input/output (I/O) devices  26  and various memory subsystems coupled to the processor  22  either directly or by way of a chipset  28 . In the illustrated example, the memory subsystems include a random access memory (RAM)  30  and  31  such as a fast page mode (FPM), error correcting code (ECC), extended data output (EDO) or synchronous dynamic RAM (SDRAM) type of memory, and may also be incorporated in to a single inline memory module (SIMM), dual inline memory module (DIMM), small outline DIMM (SODIMM), and so on. For example, SODIMMs have a reduced packaging height due to a slanted arrangement with respect to the adjacent circuit board. Thus, configuring the RAM  30  as a SODIMM might be particularly useful if the system  20  is part of a notebook PC in which thermal constraints are relatively tight. SODIMMs are described in greater detail in U.S. Pat. No. 5,227,664 to Toshio, et al. 
     The memory subsystems may also include a read only memory (ROM)  32  such as a compact disk ROM (CD-ROM), magnetic disk, flash memory, etc. The illustrated RAM  30 ,  31  and ROM  32  include instructions  34  that may be executed by the processor  22  as one or more threads. The ROM  32  may be a basic input/output system (BIOS) flash memory. Each of the RAM  30 ,  31  and/or ROM  32  are able to store a configuration table  36  that can be used to select maximum operating points. The table  36 , which may be calculated “on the fly” by software or pre-stored in memory, can be similar to the Table I discussed above. In this regard, the activity module  14 ′ may include a configuration table input  38  to be used in accessing the configuration table  36 . 
     As already discussed, the activity module  14 ′ is able to determine the number of active cores in the plurality of processor cores  12 ′. The activity can be determined by monitoring a state signal  40  ( 40   a - 40   n ) of each of the plurality of processor cores  12 ′ and identifying whether each state signal  40  indicates that the corresponding core is active. For example, the activity module  14 ′ could monitor an Advanced Configuration and Power Interface (e.g., ACPI Specification, Rev. 3.0, Sep. 2, 2004; Rev. 2.0c, Aug. 25, 2003; Rev. 2.0, Jul. 27, 2000, etc.) processor power state (“Cx state”) signal of each of the plurality of processor cores  12 ′. ACPI Cx states are relatively unproblematic to monitor and therefore provide a useful solution to determining the number of active cores. 
     ACPI defines the power state of system processors while in the working state (“G0”) as being either active (executing) or sleeping (not executing), where the power states can be applied to each processor core  12 ′. In particular, processor power states are designated as C0, C1, C2, C3, . . . Cn. The shallowest, C0, power state is an active power state where the CPU executes instructions. The C1 through Cn power states are processor sleeping states where the processor consumes less power and dissipates less heat than leaving the processor in the C0 state. While in a sleeping state, the processor core does not execute any instructions. Each processor sleeping state has a latency associated with entering and exiting the state that corresponds to the state&#39;s power savings. In general, the longer the entry/exit latency, the greater the power savings when in the state. To conserve power, an operating system power management (OSPM) module (not shown) places the processor core into one of its supported sleeping states when idle. 
     The state signals  40  can also include information regarding performance levels. For example, the state signals  40  may indicate the performance level of each active core. Such a signal could be provided by ACPI performance state (Px state) signals. In particular, while in the C0 state, ACPI can allow the performance of the processor core to be altered through a defined “throttling” process and through transitions into multiple performance states (Px states). While a core is in the P0 state, it uses its maximum performance capability and may consume maximum power. While a core is in the P1 state, the performance capability of the core is limited below its maximum and consumes less than maximum power. While a core is in the Pn state, the performance capability of core is at its minimum level and consumes minimal power while remaining in an active state. State n is a maximum number and is processor or device dependent. Processor cores and devices may define support for an arbitrary number of performance states not to exceed 16 according to the ACPI Specification, Rev. 3.0. 
     Thus, if the illustrated activity module  14 ′ monitors sleep state signals  40 , it can identify whether each sleep state signal  40  indicates that the corresponding core is active. The activity module  14 ′ can then search the configuration table  36  for an entry containing the number of active cores. A similar search could be conducted with respect to performance levels. Upon finding the entry, the activity module  14 ′ may retrieve a maximum operating point, via the configuration table input  38 , from the entry, where the maximum operating point enables a parameter such as frequency or core voltage to be limited. 
     For example, the activity module  14 ′ can generate a limit request  42  based on the maximum operating point. As already noted, the limit request  42  may specify a maximum operating frequency and/or maximum core voltage. Thus, as the active cores submit operating point requests to the controller  24 , the controller  24  ensures that none of the operating points exceed the maximum operating point specified in the limit request  42 . Simply put, the controller  24  can limit the appropriate parameter of the active cores based on the limit request  42 . 
     Although the illustrated system  20  includes a processing architecture that contains a single package/socket, multi-core processor  22 , the embodiments of the invention are not so limited. For example, a first subset of the plurality of processor cores  12  could be contained within a first processor package and a second subset of the plurality of processor cores  12  could be contained within a second processor package. Indeed, any processing architecture in which performance predictability and/or power management are issues of concern can benefit from the principles described herein. Notwithstanding, there are a number of aspects of single package/socket, multi-core processors for which the system  20  is well suited. 
     Turning now to  FIG. 3 , a method  44  of managing operating points is shown. The method  44  may be implemented in fixed functionality hardware such as complementary metal oxide semiconductor (CMOS) technology, microcode, software such as part of an operating system (OS), or any combination thereof. Processing block  46  provides for determining the number of active cores in a plurality of processor cores and/or the performance level of each of the active cores. A maximum operating point is selected for the active cores at block  48  based on the number of active cores and/or the active core performance level(s). Block  50  provides for generating a limit request based on the maximum operating point, where an operating parameter of the cores can be limited based on the limit request. The limit request may specify a maximum operating frequency and/or maximum operating voltage. 
       FIG. 4  shows one approach to determining the number of active cores in greater detail at block  46 ′. In particular, the illustrated block  52  provides for monitoring a sleep state signal of each of the plurality of processor cores. As already discussed, the sleep state signals may be ACPI Cx state signals. If the monitoring at block  52  is to include monitoring performance state data, the signals may be ACPI Px state signals. Block  54  provides for identifying whether each sleep state signal indicates that a corresponding core is active. 
     Turning now to  FIG. 5 , one approach to selecting a maximum operating point is shown in greater detail at block  48 ′. In the example shown, the maximum operating point is selected based on the number of active cores. Alternatively, the selection could be based on the performance level of each active core. In particular, the illustrated block  56  provides for searching a configuration table for an entry containing the number of active cores. In one embodiment, the searching is conducted on a BIOS configuration table. The maximum operating point is retrieved from the entry at block  58 . Alternatively, the maximum operating points could be calculated. Such an approach may be particularly useful if the selection of maximum operating points is based on active core performance levels. For example, the calculation could involve an averaging (weighted or unweighted) of core operating frequencies. A weighted average may be particularly useful in systems having non-symmetrical cores (i.e., large and small cores in the same system) because the larger cores could be given a greater weight due to their potentially greater contribution to the overall power consumption. 
     Thus, the embodiments described herein can provide for the constraining of power in multi-core processing architectures while providing predictable performance throughout most of the architecture&#39;s power range. By dynamically adjusting the maximum frequency and voltage operating point to the number of active cores in the architecture, these solutions offer a coarse-grained mechanism that can be used as a stand-alone technique or as a complement to traditional temperature-based throttling techniques. 
     Those skilled in the art can appreciate from the foregoing description that the broad techniques of the embodiments of the present invention can be implemented in a variety of forms. Therefore, while the embodiments of this invention have been described in connection with particular examples thereof, the true scope of the embodiments of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and following claims.

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