Abstract:
A system and method are provided to improve power efficiency of processor cores, such as processor cores in a multicore processor. A break-even time of a processor core may be determined that affects which power saving mode a processor core should enter when an expected idle of the processor core is identified. The break-even time of the processor core may be determined during run-time to help determine an applicable power saving mode that improves power efficiency of the processor core.

Description:
1. TECHNICAL FIELD 
     This disclosure relates to multicore processors. More particularly, this disclosure relates to managing power consumption of processor cores of a multicore processor. 
     2. BACKGROUND 
     Continual development and rapid improvement in modern technology has resulted in the widespread availability and use of electronic devices. Electronic devices are used in nearly every facet of life today. Electronic device and component manufacturers are continually developing additional features and functionality that consume power at increasing rates. As electronic devices become increasingly portable and functionally powerful, manufacturers and consumers have an increasing interest in improving the power efficiency of electronic devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The innovation may be better understood with reference to the following drawings and description. In the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  shows a power loss timing example of a processor. 
         FIG. 2  shows an exemplary system for dynamically managing power control over a processor core. 
         FIG. 3  shows an exemplary system for dynamically managing power control over processor cores of a multicore processor. 
         FIG. 4  shows an exemplary system for dynamically managing power control over processor cores of multicore processors. 
         FIG. 5  shows exemplary tables that may be used to dynamically calculate the power control break-even time of processor cores of multicore processors. 
         FIG. 6  shows power control logic that a system may implement as hardware, software, or both. 
         FIG. 7  shows power control logic that a system may implement as hardware, software, or both. 
         FIG. 8  shows various exemplary power loss timing diagrams. 
     
    
    
     DETAILED DESCRIPTION 
     Power loss in an integrated circuit (“IC”) such as a processor core may occur for multiple reasons. Generally, power loss in an IC may be characterized as either dynamic dissipation that may occur because of switching variation or as static dissipation that may occur as a result of leakage current that is present even in the absence of switching variation. Such static power dissipation as a result of leakage current may also be referred to as leakage power, and may occur as long as the processor core is powered on. Processor cores may enter into various power management modes in order to control and minimize power loss. 
     The discussion below makes reference to power control break-even time, which may be better understood through  FIG. 1 .  FIG. 1  shows a power loss timing example  100  of a processor core. The power loss timing example  100  depicts the processor operating in varying modes at different points in time. Prior to time t 1  and subsequent to time t 4  represent times when processor core may operate in a normal execution mode (e.g., a mode in which no particular power management mode is applicable, applied, or enforced on the processor core). 
     Between time t 1  and t 4 , the power loss timing example  100  shows power loss of the processor core according to two power management modes PM 1  and PM 2 . There may be additional and different power management modes defined in the system that includes the processor cores. The power management modes described below are examples only. 
     A first power management mode (PM 1 ) may be implemented by stopping switching variation of the processor core. For example, gating the clock of the processor core may operate to halt variation in the processor core, thereby limiting dynamic dissipation of power in the processor core. However, stopping switching variation of the processor core through the first power management mode may still result in power loss. As the processor core is still powered on (e.g., because one or more operational voltage(s) are still applied to the processor core), the processor core may continue to experience power loss in the form of leakage power. In the example of  FIG. 1 , the processor core enters into the first power management mode PM 1  from time t 1  to t 4 . The power lost by the processor core during this time can be represented by the PM 1  lost leakage power  110 . In one implementation, the lost leakage power may be determined as the leakage power rate of the processor core multiplied by the time the processor core is in the first power management mode PM 1 . 
     As is also illustrated in  FIG. 1 , a second power management mode PM 2  may be implemented by powering off the processor core. Powering off the processor may be accomplished by, for example, removing or disconnecting one or more operational voltage(s) normally applied to the processor core, by substantially reducing one or more operational voltage(s), or in other ways. During the time the processor core is powered off, the processor core typically experiences little, if any, power loss, and in particular, the leakage power loss is significantly reduced if not completely eliminated. However, powering off a processor core may result in losing state information associated with the processor core, such as information stored in volatile memory incorporated or associated with the processor core, such as an L1 cache or an L2 cache. Thus, when entering into the second power management mode PM 2 , the processor core may execute shut down actions, such as preserving the memory state of the processor core. For example, the processor core may preserve memory state by storing the contents of the L1 cache or the L2 cache into another memory, such as a Random-Access Memory (“RAM”) or an external memory. Additional shut down actions may be implemented beyond memory preservation actions. Similarly, when the processor core begins to exit the second power management mode PM 2 , the processor core may execute wake up actions, such as restoring the memory state of the processor core or other wake up actions that may correlate with shut down actions. 
     These additional actions taken to shut down and wake up by the processor core result in power loss based on switching variation to execute the additional shut down and wake up actions as well as any leakage power that occurs in the time it takes the processor core to execute the additional memory-related actions. Thus, as seen in  FIG. 1 , the processor core may begin the power management mode PM 2  at time t 1 , and exit the power management mode PM 2  at time t 4 . Although the second power management mode PM 2  extends from time t 1  to t 4 , power is still spent when the processor executes shut down actions from time t 1  to time t 2  and wake up actions from time t 3  to t 4 . The power lost by the processor core during this time can be represented by the sum of the PM 2  lost active and leakage power  120 , which represents the amount of power dissipated by executing shut down actions to preserve the memory state of the processor core, depicted between time t 1  and t 2  and the PM 2  lost active and leakage power  121 , which represents the amount of power dissipated by executing wake up actions to restore the memory state of the processor core, depicted between t 3  and t 4 . 
     In some implementations, a power control break-even time may be determined as a time duration at which more power can be saved by using a particular power mode over another different power mode. With respect to PM 1  and PM 2 , for example, the power control break-even time may be determined as the amount of time needed for the PM 1  lost leakage power  110  to equal to the sum of the PM 2  shut down lost active and leakage power  120  and the PM 2  start up lost active and leakage power  121 . Phrased alternatively, in some implementations, the power control break-even may be a time duration that makes the amount of power lost by the processor core under the first power management mode PM 1  the same as the amount of power lost by the processor core under the second power management mode PM 2 . 
     As described above, it becomes apparent that the longer the amount of time a processor core remains in the first power management mode PM 1 , the more the accumulated power loss increases due to the persistent nature of leakage power. In contrast, regardless of the amount of time a processor core remains in the second power management mode PM 2 , the power lost by the processor remains constant or approximately constant. Thus, if the processor core is to enter one of the power management modes for an amount of time less than the power control break-even time of the processor core, then entering the first power management mode PM 1  may result is less power loss than entering the second power management mode PM 2 . On the other hand, if the processor core is to enter one of the power management modes for an amount of time greater than the power control break-even time, entering the second power management mode PM 2  may result in less power loss than entering the first power management mode PM 1 . Power accumulation comparisons are illustrated in  FIG. 8  and described below. 
     Various factors may affect the power control break-even time of a processor core. First, the shut down and wake up actions executed in connection with entering the second power management mode PM 2  may affect the power control break-even time of the processor core. Additional shut down and wake up actions, such as saving processor state in multiple locations (e.g., DDR RAM or an external memory), may affect the power control break-even time. Further, additional circuitry that may be powered off when entering the second power management mode PM 2  may also affect the break-even time. For example, the second power management mode PM 2  may be implemented by powering off the processor core and memory associated with the processor core, such as an L1 cache or an L2 cache. In this case, additional shut down actions may be executed to preserve the state of the processor core, such as saving the contents of the L1 cache or the L2 cache. Corresponding additional wake up actions may be included in the second power management mode PM 2  as well. As the L1 cache or the L2 cache may be powered down when entering power management mode PM 2 , the leakage power of the L1 cache or the L2 cache may also be accounted for when determining the power loss of power management mode PM 1 . 
     Another factor that may affect the power control break-even time of a processor core is the performance level the processor core operates at. The processor core may operate at varying performance levels, which may be discrete performance levels. For example, a processor core may operate at an economy performance level with a first clock frequency, a normal performance level with a second frequency faster than the first clock frequency, and a turbo performance level with a third clock frequency faster than the first and second clock frequencies. For each performance level, the processor core may execute the shut down and wake up actions of the second power management level PM 2  at different speeds but also with different power consumption over a given period. For example, if the processor core enters the second power management mode PM 2  while operating at an economy performance level, the processor may take a longer time to execute the shutdown actions, resulting in higher leakage power lost as compared to the shorter time to execute the shutdown actions in the turbo performance level. However, the dynamic power loss from executing the shutdown actions in the turbo performance level may be higher due to the higher power cost to execute instructions at the higher clock frequency. Thus, performance level of a processor core may affect the processor core&#39;s power control break-even time. 
     As another example, the power control break-even time may be affected by leakage power characteristics of the processor core, which may vary from core to core of the same processor core type. The fabrication parameters used in manufacturing the processor core may affect the power control break-even time, as such parameters may affect the switching speed of the processor core. Process-Voltage-Temperature (PVT) variation effects, which may vary from processor core to processor core, may also affect the calculation of a power control break-even time. Thus, the power control break-even time of a processor core manufactured according to typical-typical (“TT”) fabrication parameters may be different from the power control break-even time of the type of processor core manufactured according to fast-fast (“FF”) fabrication parameters. 
     Aging effects that change properties of the processor core over time may also affect the leakage power of a processor core, thereby affecting the power control break-even time of the processor core. Thus, the power control break-even time of the same processor core may be different at differing points in time. Each of the above-described factors may affect the calculation and subsequent use of the power control break-even time of a processor. 
       FIG. 2  is an example of a system  200  for dynamically managing power control over a processor core. To that end, the system  200  may determine power control break-even times of the processor core as part of its operation. In this example, the system  200  includes a processor core  210  that includes an L1 cache  220 . The system  200  also includes a variation monitor  230  and evaluation logic  240 . The variation monitor  230  is communicatively coupled to the processor core  210 , and the evaluation logic  240  is communicatively coupled to the variation monitor  230  and the processor core  210 . 
     In operation, the evaluation logic  240  may instruct the variation monitor  230  to obtain an evaluation of or capture the leakage power behavior of the processor core  210 , for example by measuring a variation indicator of the processor core  210 . The variation monitor  230  may measure the variation indicator of the processor core  210  during run-time, for example when the processor core  210  initially boots up. Also, the variation monitor  230  or the evaluation logic  240  may instruct the processor core  210  to perform a predetermined action so that the variation monitor  230  can measure a variation indicator from the processor core  210 . As one example, the evaluation logic  240  or the variation monitor  230  may instruct the processor core  210  to execute a save and restore operation using the L1 cache  220 , during which the variation monitor  230  may measure a variation indicator of the processor core  210 . 
     The variation indicator may indicate leakage power behavior of the processor core  210  during run time. In other words, the variation indicator captured by the variation monitor  230  may be reflective or show properties of the processor core  210  that may affect determination of a power control break-even time of the processor, including, for example, PVT variations, fabrication parameters, properties during run-time (e.g., core temperature), and aging effects of the processor core  210 . The variation monitor  230  may include logic or hardware that is physically connected to or located within each processor core (e.g., the processor  210 ) the variation monitor  230  is connected to in order to measure the variation indicator. As one example, the variation monitor  230  may be silicon performance monitor (“SPM”) hardware and logic. A SPM may measure the total toggle counts of ring-oscillator which are generally affected by PVT variations, fabrication parameters, aging effects, and other processor properties that may affect the determination of a the power control break-even time for the processor  210 . 
     As described above, the power control break-even time of the processor core  210  may vary depending on the performance level of the processor core  210 . Accordingly, the evaluation logic  240  may instruct the variation monitor  230  to measure a variation indicator of the processor core  210  for each performance level the processor core  210  may operate at. To illustrate, the evaluation logic  240  may instruct the processor core  210  to perform a predetermined set of actions at varying performance levels, for example executing a save and restore operation using the L1 cache three times—first at an economy performance level, second at a normal performance level, and third at a turbo performance level. The variation monitor  230  may measure three variation indicators from the processor core  210 , one for each performance level. If the processor core  210  can operate in N number of performance levels, the variation monitor  230  may measure up to N number of variation indicators. 
     Upon measuring a variation indicator of the processor core, The evaluation logic  240  may determine a power control break-even time based on a measured variation indicator. For example, the evaluation logic  240  may map the measured variation indicator to a power control break-even time, as described in greater detail below. The evaluation logic  240  may determine a respective power control break-even time for each performance level the processor core  210  can operate in. 
     Next, the evaluation logic  240  may obtain an expected idle time of the processor core, for example from logic external to the system  200 . The evaluation logic  240  may then determine an applicable power saving mode for the processor core  210  based on the current performance level of the processor core  210 , the expected idle time, and the applicable power control break-even time. For example, if the expected idle time is less than the power control break-even time, the evaluation logic  240  may instruct the processor core  210  to enter into a first power management mode, such as power management mode PM 1  described above. If the expected idle time is greater than the power control break-even time, the evaluation logic  240  may instruct the processor core  210  to enter into a second power management mode, such as power management mode PM 2  described above. 
     As shown in  FIG. 2 , the evaluation logic  240  may be implemented as a power manager  250  and a memory  252 . The power manager  250  may be implemented as hardware, software, or both. For example, the power manager  250  may be implemented as a microcontroller, including a microcontroller processor, microcontroller memory and microcontroller instructions or as a processor and memory storing processor executable instructions. The power manager  250  may be communicatively coupled to the memory  252 , and the memory  252  may include a variation table  260  and a mapping table  270 . The evaluation logic  240  may also store a current power control break-even time of the processor core  210  in a register or in a location in the memory  252 . In operation, the power manager  250  may apply a power management mode to the processor core  210  based on a power control break-even time, as discussed above. In doing so, the power manager  250  may reference or update the variation table  260 . The power manager  250  may also reference the mapping table  270 . 
     The variation table  260  may store variation indicator information of a processor core, such as variation indicators of the processor core  210  measured by the variation monitor  230 . The variation table  260  in  FIG. 2  includes a variation table entry  262 . The variation table entry  262  includes a processor core ID field  264 , a first performance level variation indicator field  266 , a second performance level variation indicator field  267 , and a third performance level variation indicator field  268 . The processor core ID field  264  may identify the processor core that the variation table entry  262  stores variation indicator information for. In  FIG. 2 , the variation table entry  262  stores variation indicator information for Core 0. The first performance level variation indicator field  266  may store the variation indicator measured by the variation monitor  230  when the processor core  210  was operating in an economy performance level, such as the variation indicator  60 , as show in  FIG. 2 . Similarly, the second performance level variation indicator field  267  may store variation indicator information measured when the processor core  210  was operating in normal performance level and the third performance level variation indicator field  268  may store variation indicator information measured when the processor core  210  was operating in turbo performance level. Thus, the variation table entry  262  indicates that the variation monitor  230  measured a variation indicator of  60  when the processor core  210  was operating in economy,  80  when operating in normal, and  105  when operating in turbo. 
     The power manager  250  may update entries in the variation table  260  whenever the variation monitor  230  measures a variation indicator of the processor core  210 . As discussed above, the variation monitor  230  may measure variation indicators when the processor core  210  initially boots up. Alternatively, the power manager  250  may instruct the variation monitor  230  to measure variation indicators of the processor core  210  at fixed intervals, such as once every two milliseconds, or when instructed by other systems or logic in communication with the power manager  250 . The power manager  250  may update (or create) the applicable entry in the variation table  260  whenever such variation indicator measurements are conducted. 
     The power manager  250  may reference the variation table  260  and the mapping table  270  in order to determine a power control break-even time of the processor core  210 . As depicted in  FIG. 2 , the mapping table  270  includes the mapping table entries  271 - 275 . The mapping table entry  275  includes a variation indicator field  282  and a power control break-even time field  284 . Each of the mapping table entries  271 - 275  may associate a variation indicator with a power control break-even time for a processor core, such as the processor core  210 . Thus, according to the mapping table entry  275  in  FIG. 2 , for the processor core  210 , a variation indicator of  60  corresponds to a power control break-even time of 5 ms. A variation indicator of  80  corresponds to a power control-even time of 6 ms, etc. 
     Entries in the mapping table  270  may be generated through extensive simulations. That is, behavior of the processor core  210  may be simulated to determine how variation indicators of the processor core  210  correlate to a power control break-even time. The extensive simulations may involve measuring power loss in the processor core in the first power management mode PM 1  and the second power management mode PM 2  according to any number of processor configurations or variation parameters. The simulations may also incorporate other factors affecting the power control break-even time calculation, such as any of the factors discussed above that affect the power control break-even time of a processor. The simulations may also account for the particular shut down actions and what wake up actions are executed by the processor core when entering and existing a second power management mode PM 2 . As another example, simulations may involve changing the voltage and temperature values for processors cores fabricated at each processor corner and determining the power control break-even time based on each scenario. 
     The power manager  250  may determine a power control break-even time of the processor core  210  by referencing the variation table  260  and the mapping table  270 . For example, when the processor core  210  is operating in an economy performance level, the power manager  250  may reference the variation table  260  to determine that a variation indicator of  60  was measured for economy level operation. The power manager  250  may then reference the mapping table  270 , specifically mapping table entry  282 , to determine that the current power control break-even time of the processor core  210  operating in an economy performance level is 5 ms. 
     If the exact variation indicator value in a variation table entry is not stored as part of an entry in the mapping table  270 , then the power control break-even time may be extracted from other mapping table entries. For example, the power manager  250  may determine that the measured variation indicator for a turbo performance level of the processor core  210  is  105 . The mapping table  270  does not include an entry that includes a variation indicator of  105 . Instead, the mapping table entry  273  maps a variation indicator of  100  to a power control break-even time of 8 ms and the mapping table entry  272  maps a variation indicator of  120  to a power control break-even time of 10 ms. Thus, the power manager  250  may determine that the current power control break-even time of the processor core  210  operating at a turbo performance level is somewhere between 8 ms and 10 ms. As one example, the power manager  250  may determine a power control break-even time for the processor core  210  with the variation indicator of  105  by linearly interpolating between the two mapping table entries, resulting in a power control break-even time of 8.5 ms. Alternatively, the power manager  250  may apply a “worst-case scenario” determination policy, determining that the power control break-even time is 10 ms. 
     Once the power control break-even time of the processor core is determined, the power manager  250  may obtain an expected idle time, and apply a power management mode to the processor core  210  based on the current performance level, the expected idle time, and the power control break-even time. 
       FIG. 3  shows an exemplary system  300  for dynamically managing power control over processor cores of a multicore processor. To that end, the system  300  may determine power control break-even times of the processor cores of the multicore processor as part of its operation. The system  300  includes a multicore processor  305 . The multicore processor  305  includes the processor cores  310 ,  312 ,  314 , and  318 , which each include a corresponding L1 cache (L1 caches  311 ,  313 ,  315 , and  317  respectively). The multicore processor  305  also includes an L2 cache  320 , communicatively coupled to each of the processor cores  310 ,  312 ,  314 , and  316 . The system  300  also includes a power manager  250  and a memory  252 . The memory  252  includes a current power control break-even time table  350 , a variation table  360 , and a mapping table  370 . 
     In operation, the processor cores  310 ,  312 ,  314 , and  316  may store and read data from the L2 cache  320 . The power manager  250  may measure variation indicators for varying processor core performance levels, update or reference the variation table  360 , reference the mapping table  370 , and determine a power control break even time for each of the processor cores  310 ,  312 ,  314 , and  316  in a similar manner as described in  FIG. 2 . The power manager  250  may also apply a power management mode to the processor core  310 , the processor core  312 , the processor core  314 , or the processor core  316  based on the current power control break-even time of the processor core, the performance level the processor core is operating at, and an expected idle time of the processor core. 
     The current power control break-even time table  350  may include a current power control break-even time entry  351  that may store the current power control break even time of each processor core of the multicore processor  305 . The current power control break-even time entry  351  may include a first field  352  that stores the current power control break-even time of the processor core  310 , a second field  353  that stores the current power control break-even time of the processor core  312 , a third field  354  that stores the current power control break-even time of the processor core  314 , and a fourth field  355  that stores the current power control break-even time of the processor core  316 . The power manager  250  may update the current power control break-even time of a processor core when the processor core changes performance level. For example, if the processor core  310  changes performance level from economy to turbo, the power manager  250  may determine the power control break-even time of the processor core  310  when operating in a turbo performance level. Then, the power manager  250  may update the first field  352  of the current power control break-even time entry  351  to reflect the change in performance level of the processor core  310 . 
     In one implementation, the power manager  250  may use the power control break-even time of a processor core to determine an applicable power management mode when no other processor cores of the multicore processor  305  are active. Additional processor power management logic (not pictured) may be used to control power management of the processor cores  310 ,  312 ,  314 , and  316  when multiple cores are active. For example, when performance needs of the multicore processor  305  are reduced, the additional processor power management logic may power off a processor core based on performance requirements and without referencing the power control break-even time of the processor core. Thus, in this implementation, the power manager  250  may update the current power control break-even time of a processor core when no other processor cores are active, but not when other processor cores are active. Also, to update the variation table  360 , the power manager  250  may instruct the variation monitor  230  to measure a variation indicator for each performance level of the processor core  310  when no other processors are active. This can be done in order to model leakage power behavior during conditions when the power control break-even time would be applied (e.g., when no other processors are active). Similar variation indicator measurements may be measured for the processor cores  312 ,  314 , and  316  as well. The variation indicator information measured from the processor cores  310 ,  312 ,  314 , and  316  may be stored in the variation table  360 . 
     As discussed above, a processor core entering a second power management mode PM 2  may perform shut down actions whereupon the processor core is powered off. In one implementation for the system  300  including the multicore processor  305 , the second power management mode PM 2  may be adjusted to also include powering off the L2 cache. In one implementation, the adjusted second power management mode PM 2  may be applicable when a processor core is entering the adjusted second power management mode PM 2  when no other processor cores are active. To illustrate, the processor core  310  may be the only active processor core in the multicore processor  305 . As a result, the processor  310  may be the only processor core in the multicore processor  305  using the L2 cache  320 . 
     Thus, if the power manager  250  identifies expected idle time for the processor core  310 , the L2 cache  320  may also be powered off without affecting the performance or functionality of the other processor cores  312 ,  314 , and  316 . As a result, the second power management mode PM 2  may be adjusted such that the shutdown actions also include preserving the contents of the L2 cache  320 , for example by copying the contents of the L2 cache to a Random Access Memory 380. The wake up actions of the second power management mode PM 2  may also be adjusted to include restoring the contents of the L2 cache  320  upon wakeup. Also, the power loss calculation for the first power management mode PM 1  may be adjusted to include the leakage power rate of both the processor core  310  and the L2 cache  320 . These changes in the power management modes PM 1  and PM 2  may affect the calculation of the power control break-even time of the processor core  310 . These factors may be incorporated into the simulations used to generate the mapping table  370  and reflected in the entries  371 - 375  of the mapping table  370 . 
     The power manager  250  may identify expected idle time for a processor core. The power manager  250  may then apply a power management mode to the processor core based on the expected idle time and the current power control break-even time of the processor core. 
       FIG. 4  shows an exemplary system  400  for dynamically managing power control over processor cores of multicore processors. To that end, the system  400  may determine power control break-even times of the processor cores of the multicore processors as part of its operation. The system  400  depicted in  FIG. 4  includes a multicore processor  405  that includes two processor cores  410  and  412  and a multicore processor  305  that includes four processor cores  310 ,  312 ,  314 , and  316 . The multicore processors  405  and  305  may be communicatively coupled to a L3 Cache  430 . 
     The system  400  also includes a power manager  250  that may apply power management modes to the processor cores  410 ,  412 ,  310 ,  312 ,  314 , and  316  of the multicore processors  405  and  305 . To that end, the power manager  250  may be communicatively coupled to a memory  252  that includes a variation table  460  and a mapping table  470 . The memory  252  may also include a current power control break-even time table (not pictured) that stores the current power control break-even time for each of the processor cores in the system  400 . 
     In operation, the power manager  250  may apply power management modes to processor cores of the multicore processor  305  or the multicore processor  305  in a similar way as described in  FIG. 3  above. In one implementation, the power manager  250  may manage power management modes for processor cores of the multicore processor  405  separately from processor cores of the multicore processor  305 . For example, the power manager  250  may manage power management modes for the processor cores  310 ,  312 ,  314 , and  316  of the multicore processor  305  in a similar way as detailed in  FIG. 3 , which did not depict an additional L3 cache  430  or the multicore processor  405 . Alternatively, the power manager  250  may manage power management modes by considering the cores of the multicore processors  405  and  305 . For example, the power manager  250  may use the power control break-even time of a processor core to determine an applicable power management mode when no other processor cores of either the multicore processor  305  or the multicore processor  405  are active. In this situation, a second power management mode PM 2  may be further adjusted to account for powering off the L3 cache  430  in a similar way as described in adjusting the second power management mode PM 2  to account for powering off an L2 cache as described above. 
     To account for managing power management modes of the multicore processor  305  and the multicore processor  405 , the variation table  460  may include separate portions for each multicore processor. The variation table  460  depicted in  FIG. 4  includes a multicore processor  1  portion  461  that may store variation indicator information for the multicore processor  305  and a multicore processor  2  portion  462  that may store variation indicator information for the multicore processor  405 . 
     Similarly, the mapping table  470  may include separate portions for each multicore processor managed by the power manager  250 . As an example, the mapping table  470  depicted in  FIG. 4  includes a multicore processor  1  portion  471  that may store variation indicator to power control break-even time mappings for the multicore processor  305  and a multicore processor  2  portion  472  that may store variation indicator to power control break-even time mappings for the multicore processor  405 . 
       FIG. 5  shows exemplary tables  500  that may be used to dynamically calculate the power control break-even time of processor cores of multicore processors. The exemplary tables  500  include a variation table  460  and a mapping table  470 . The variation table  460  includes variation table entries  510 - 515 . The mapping table  470  includes mapping table entries  530 - 539 . 
     The variation table  460  may be arranged similarly to the variation table  260  described in  FIG. 2  above. However, as the variation table  460  may store variation indicator information for multiple processors, such as the multicore processor  305  and the multicore processor  405 , entries in the variation table  460  (e.g., variation table entries  510 - 515 ) may include an additional field identifying the processor the entry is associated with. To illustrate, the variation table entry  515  may include a processor ID field  521 , processor core ID field  522 , a first performance level variation indicator field  523 , a second performance level variation indicator field  524 , and a third performance level variation indicator field  525 . The processor ID field  521  in variation entry table  515  may store a value of 2, indicating this entry is associated with processor  2 , that is multicore processor  405 . Thus, variation table entry  514  may store variation indicator information for the processor core  410  of the multicore processor  405  and variation table entry  515  may store variation indicator information for processor core  412  of the multicore processor  405 . Variation entries  510 - 513  may respectively store variation indicator information for the processor cores  310 ,  312 ,  314 , and  316  of the multicore processor  305  in a similar way. 
     The mapping table  470  may be arranged similarly to the mapping table  270  described in  FIG. 2  above. Mapping table entries  530 - 539  may associate a variation indicator with a power control break-even time for processor cores of the multicore processor  305  or the multicore processor  405 . Thus, entries in the mapping table  470  may include an additional field not included in the mapping table  270  to identify the processor the entry is associated with. To illustrate, the mapping table entry  539  includes a processor ID field  541 , a variation indicator field  542 , and a power control break-even time field  543 . The processor ID field  541  may store a value of 2, indicating the mapping table entry  539  is associated with the multicore processor  405 . Similar fields in mapping table entries  535 - 539  may also indicate these entries are associated with the multicore processor  405 . In the same way, mapping table entries  530 - 534  may be associated with the multicore processor  305 . 
     In operation, the power manager  250  may reference or update a corresponding entry of the variation table  460  depending on which processor, which processor core, and which performance level the updated or referenced variation indicator information relates to. Similarly, the power manger  250  may reference a corresponding entry or entries in the mapping table  470  depending on the processor and variation indicator. 
       FIG. 6  shows power control logic  600  that the system  200  may implement as hardware, software, or both. For example, the power control logic  600  may be implemented in the power manager  250 . The power manager  250  may instruct a variation monitor  230  to measure a variation indicator of a processor core ( 602 ). If the processor core can operate at multiple performance levels, the power manager  250  may instruct the variation monitor  230  to measure a variation indicator for each performance level. For example, when the processor core starts up, the power manager  250  may instruct the processor core to execute a set of actions at each performance level, whereupon the variation monitor  230  may measure a variation indicator. The power manager  250  may receive the measured variation indicator(s) from the variation monitor  230  ( 604 ). Next, the power manager  250  may update a variation table  260  to reflect the measured variation indicators ( 606 ). 
     After updating the variation table  260 , the power manager  250  may determine when the processor core next becomes active ( 608 ). For example, after performing variation during for measuring variation indicators at boot time, the processor core may be inactive until a later time. When the processor core becomes active, the processor core may operate at a performance level. The power manager  250  may determine the power control break-even time of the processor core ( 610 ). For example, as described above, the power manager  250  may reference the variation table  260  and the mapping table  270  to determine a power control break-even time for the processor core operating at the performance level. The power manager  250  may then assign a current power control break-even time to the processor core ( 612 ). 
     The power manager  250  may determine if the processor core changes performance level ( 614 ). If so, the power manager  250  may update the current power control break-even time of the processor core ( 616 ). The power manager  250  may similarly determine the power control break-even time of the performance level the processor core changed to by referencing the variation table  260  and the mapping table  270 . 
     If the power manager  250  does not determine the processor core changed performance, the power manager  250  may identify an expected idle time of the processor core ( 618 ). Expected idle time may be identified in different ways. For example, if the processor core is processing a music file, the power manager  250  or additional logic may identify expected idle time based on the sampling frequency the music file is encoded in. For example, if sampling the music file requires 2 ms of processing time by the processor core every 10 ms, then the power manager  250  may identify 8 ms of expected idle time after performing the 2 ms of music sampling processing. In one implementation, expected idle time is determined by additional logic external to the power manager  250 , whereupon the expected idle time is then received by the power manager  250 . 
     If the power manager  250  does not identify or receive an expected idle time, then the power manager  250  may continue to monitor whether the processor core changes performance level ( 614 ) or identifies or receives an expected idle time ( 618 ). If the power manager  250  identifies or receives an expected idle time, the power manager  250  may apply a power management mode to the processor core based on the current power control break-even time and the expected idle time ( 620 ). 
       FIG. 7  shows power control logic  700  that the system  400  may implement as hardware, software, or both. For example, the power control logic  700  may be implemented in a power manager  250  that manages power management modes of processor cores in multicore processors. A power manager  250  may instruct a variation monitor  230  to measure variation indicators for each processor core of each multicore processor in a system ( 702 ). If any processor cores of any multicore processor can operate at multiple performance levels, the power manager  250  may instruct the variation monitor  230  to measure each of the variation indicators for each performance level of each applicable processor core of each multicore processor. This variation indicator measurement may occur when the multicore processors first become powered on during a boot up sequence. When each multicore processor core starts up, the power manager  250  may instruct the processor core to execute a set of actions at each performance level, whereupon the variation monitor  230  may measure a variation indicator. 
     Next, the power manager  250  may receive the measured variation indicator(s) from the variation monitor  230  ( 704 ). Next, the power manager  250  may update a variation table  260  to reflect the measured variation indicators for each processor core for each multicore processor ( 706 ). 
     After the initial update of the variation table  460  during startup, the power manager  250  may then monitor when any processor core of any multicore processor becomes active, which may include identifying the performance level the activated processor core begins operating at ( 708 ). The power manager  250  may determine the power control break-even time of the activated processor core ( 710 ). For example, as described above, the power manager  250  may reference the variation table  460  and the mapping table  470  to determine a power control break-even time for the processor core operating at the performance level. The power manager  250  may then assign a current power control break-even time to the processor core ( 712 ), which may also be stored in a current power control break-even time table, such as the one described in  FIG. 3 . 
     The power manager  250  may continue to monitor if any processor cores of any multicore processor become active and determine and assign a current power control break-even time to the processor core ( 708 - 712 ). The power manager  250  may also determine if, at any point, only one processor core of a multicore processor is active ( 714 ). Or alternatively, the power manager  250  may determine if, at any point, only one processor core of multiple multicore processors is active. If so, power manager  250  may then monitor if the processor core changes performance level ( 716 ). If a performance level change occurs, the power manager  250  may update the current power control break-even time of the processor core ( 718 ), for example by referencing the variation table  260  and the mapping table  270 . 
     If only one processor core is active, the power manager  250  may also identify or receive an expected idle time of the processor core ( 720 ). If the power manager  250  does not identify or receive an expected idle time, then the power manager  250  may continue to monitor whether the processor core changes performance level ( 716 ) or identifies or receives an expected idle time ( 720 ) for as long as only one processor core remains active. 
     If an expected idle time is identified or received, the power manager  250  may apply a power management mode to the processor core based on the current power control break-even time and the expected idle time ( 722 ). If at some time another processor core becomes active ( 708 ), the power manager  250  may not apply the power manage mode to processor cores until the situation returns where only one processor core is active ( 714 ). 
       FIG. 8  shows various exemplary power loss timing diagrams  800 . The power loss timing diagrams  800  illustrate a comparison of accumulated power loss between a first power management mode PM 1  and a second power management mode PM 2  when an expected idle time is less than the power control break-even time of a processor core, is equal to the power control break-even time of a processor core, and is greater than the power control break-even time of a processor core. 
     The timing diagram at the top of  FIG. 8  illustrates a comparison of accumulated power loss between a first power management mode PM 1  and a second power management mode PM 2  when an expected idle time t 3  is less than the power control break-even time of a processor core. The first power management mode PM 1  shown in  FIG. 8  may be configured in a similar way as the first power management mode PM 1  as described in  FIG. 1  above. That is, lost leakage power in the first power management mode PM 1  may be determined as the leakage power rate of the processor core multiplied by the time the processor core is in the first power management mode PM 1 . In other words, when a processor core enters into the first power management mode PM 1  at a time t 0 , the power is lost in the form of leakage power at a steady state, as illustrated by the straight dotted line corresponding to the accumulated power lost by the first power management mode PM 1  over time. 
     The second power management mode PM 2  shown in  FIG. 8  may be configured in a similar way as the second power management mode PM 2  as described in  FIG. 1  above. The power lost by a processor core entering into the second power management mode PM 2  can be understood as the sum of the amount of power dissipated by executing shut down actions (depicted between time t 0  and t 1 ) and the amount of power dissipated by executing wake up actions (depicted between t 2  and t 3 ). As seen in  FIG. 8 , when the processor core enters into the second power management mode PM 2 , the PM 2  power loss represented by the solid line is only accumulated during execution of the shut down actions during time t 0  to t 1  and during execution of wake up actions during time t 2  to t 3 . Between time t 1  and t 2 , the processor core does not dissipate leakage power and no power is lost. As illustrated in the timing diagram at the top of  FIG. 8 , when the expected idle time is equal to the time t 3 , the power loss experienced by a processor entering into the second power management mode PM 2  is greater than the power loss experienced by the processor entering into the first power management mode PM 1 . Thus, the processor core may enter into the first power management mode PM 1  when an expected idle time is received that is less than the power control break-even time of the processor. 
     The timing diagram in the middle of  FIG. 8  illustrates a comparison of accumulated power loss between a first power management mode PM 1  and a second power management mode PM 2  when an expected idle time t 3 ′ is equal to the power control break-even time of a processor. Similar to the timing diagram at the top of  FIG. 8 , the PM 1  power loss illustrated by the dotted line increases at a steady state. Similarly, the PM 2  power loss represented by the solid line is only accumulated during execution of the shut down actions during time t 0  to t 1  and during execution of wake up actions during time t 2 ′ to t 3 ′. When the expected idle time is equal to the time t 3 ′, the power loss experienced by a processor entering into the second power management mode PM 2  is equal to the power loss experienced by the processor entering into the first power management mode PM 1 . In this case, the processor may enter either the first power management mode PM 1  or the second power management mode PM 2 . 
     The timing diagram at the bottom of  FIG. 8  illustrates a comparison of accumulated power loss between a first power management mode PM 1  and a second power management mode PM 2  when an expected idle time t 3 ″ is greater than the power control break-even time of a processor. Similar to the timing diagrams at the top and the middle of  FIG. 8 , the PM 1  power loss illustrated by the dotted line increases at a steady state. Similarly, the PM 2  power loss represented by the solid line is only accumulated during execution of the shut down actions during time t 0  to t 1  and during execution of wake up actions during time t 2 ″ to t 3 ″. When the expected idle time is equal to the time t 3 ″, the power loss experienced by a processor entering into the second power management mode PM 2  is less than the power loss experienced by the processor entering into the first power management mode PM 1 . Thus, the processor core may enter into the second power management mode PM 2  when an expected idle time is received that is greater than the power control break-even time of the processor. 
     As seen in  FIG. 8 , the length of time that elapses when the second power management mode PM 2  executes shut down actions between time t 0  and t 1  is consistent across all three timing diagrams. Similarly, the length of time that elapses when the second power management mode PM 2  executes wake up actions between time t 2  to t 3 , time t 2 ′ to t 3 ′, and time t 2 ″ to t 3 ″ respectively is also consistent across all three timing diagrams. The PM 2  power loss accumulated during execution of the shut down actions and the wake up actions in all three timing diagrams is also consistent. In other words, the accumulated power loss of a processor core entering into the second power management mode PM 2  is the same in all three timing diagrams. Thus, the power control break-even time represents the time when the PM 1  power loss that steadily increases over time equals the PM 2  power loss that is constant regardless of time. 
     The methods, devices, and logic described above may be implemented in many different ways in many different combinations of hardware, software or both hardware and software. For example, all or parts of the system may include circuitry in a controller, a microprocessor, or an application specific integrated circuit (ASIC), or may be implemented with discrete logic or components, or a combination of other types of analog or digital circuitry, combined on a single integrated circuit or distributed among multiple integrated circuits. All or part of the logic described above may be implemented as instructions for execution by a processor, controller, or other processing device and may be stored in a tangible or non-transitory machine-readable or computer-readable medium such as flash memory, random access memory (RAM) or read only memory (ROM), erasable programmable read only memory (EPROM) or other machine-readable medium such as a compact disc read only memory (CDROM), or magnetic or optical disk. Thus, a product, such as a computer program product, may include a storage medium and computer readable instructions stored on the medium, which when executed in an endpoint, computer system, or other device, cause the device to perform operations according to any of the description above. 
     The processing capability of the system may be distributed among multiple system components, such as among multiple processors and memories, optionally including multiple distributed processing systems. Parameters, databases, and other data structures may be separately stored and managed, may be incorporated into a single memory or database, may be logically and physically organized in many different ways, and may be implemented in many ways, including data structures such as linked lists, hash tables, or implicit storage mechanisms. Programs may be parts (e.g., subroutines) of a single program, separate programs, distributed across several memories and processors, or implemented in many different ways, such as in a library, such as a shared library (e.g., a dynamic link library (DLL)). The DLL, for example, may store code that performs any of the system processing described above. While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.