Abstract:
A power source control executed by a processor includes setting a plurality of period candidates indicating candidates of a predetermined period; calculating, for each of a plurality of nodes, an average interval of idle periods in which a procedure is not executed for each of the plurality of period candidates, based on operation record information indicating history of procedures; calculating an amount of reduction of power consumption with respect to each of the plurality of period candidates based on the calculated average interval and an amount of power consumption in the idle period; selecting a period that is allocated to each of the plurality of nodes from among the plurality of period candidates based on the calculated amount of reduction; and executing, for each of the plurality of nodes, control to set the power source to an off state when the idle period becomes the selected period or more.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-150574, filed on Jul. 29, 2016, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a power source control method, a power source control apparatus, and a storage medium. 
       BACKGROUND 
       [0003]    In the related art a technique is known for storing history information of a power on state and a power off state of an information processing device so that the power on state and the power off state of the information processing device are not repeated in a comparatively short period of time. According to such a technique, when a process is performed in which the power source of the information processing device is set in the off state based on stored history information, the process is held for a certain period of time. For example, Japanese Laid-open Patent Publication No. 2001-290568 is disclosed as the related art. 
         [0004]    It is considered that, in a case where the information processing device is in an idle state for a certain period of time or more, the power source is set to the off state in order to reduce an amount of power consumption of the information processing device. In the present specification, for example, the information processing device being in the idle state means, for example, that the information processing device is being activated, but a job, that is a unit of execution of a predetermined process, is in a non-executed state, and thus the power source may be set to the off state. Hereinafter the above-mentioned certain period of time, that is, a reference period in which the power source is set to the off state when the information processing device is in the idle state for this period of time or more, is referred to as a “reference idle period”. 
         [0005]    It is considered that the power source is not set to the off state until a certain period of time elapses from a time when the power source is set to the power on state last time, even if the information processing device is in the idle state so that the power on and the power off of the information processing device are not repeated in a comparatively short period of time. Hereinafter the above-mentioned certain period of time, that is, a period that is a shortest value of the period during which the power source of the information processing device is not set to the off state from a time when the power source is set to the on state even if the information processing device is in the idle state, is referred to as a “shortest activated period”. 
         [0006]    In this case, a period in which the power source of the information processing device is set to the off state according to a set value of the reference idle period changes depending on scheduling circumstances of the job. That is, in this case, a reduced amount of power consumption of the information processing device changes according to the set value of the reference idle period depending on the scheduling circumstances of the job. Accordingly, in a case where the reference idle period is set to a fixed value, there may be a case in which the amount of power consumption of the information processing device may not be more reduced than a case in which the reference idle period is set to another value depending on the scheduling circumstances of the job. In view of the above, it is desirable that the amount of power consumption of the information processing device can be reduced. 
       SUMMARY 
       [0007]    According to an aspect of the invention, a power source control executed by a processor included in a power source control apparatus, the power source control method includes setting a plurality of period candidates indicating candidates of a predetermined period used for setting a power source to an off state when a procedure is not executed in the predetermined period; calculating, for each of a plurality of nodes, an average interval of idle periods having a length of the predetermined period or more in which the procedure is not executed for each of the plurality of period candidates, based on operation record information indicating history of procedures executed in the plurality of nodes; calculating an amount of reduction of power consumption with respect to each of the plurality of period candidates based on the calculated average interval and an amount of power consumption in the idle period; selecting a period that is allocated to each of the plurality of nodes from among the plurality of period candidates based on the calculated amount of reduction; and executing, for each of the plurality of nodes, control to set the power source to an off state when the idle period becomes the selected period or more. 
         [0008]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0009]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a block diagram illustrating an outline configuration of a power source control system according to each embodiment; 
           [0011]      FIG. 2  is a diagram illustrating an example of scheduling information; 
           [0012]      FIG. 3  is a diagram illustrating an example of operation record information; 
           [0013]      FIG. 4  is a functional block diagram of a power source control apparatus according to each embodiment; 
           [0014]      FIG. 5  is a diagram illustrating an example of standby power information; 
           [0015]      FIG. 6  is a diagram for describing an example of a calculation process of a reference idle period; 
           [0016]      FIG. 7  is a block diagram illustrating an outline configuration of a computer that functions as the power source control apparatus according to each embodiment; 
           [0017]      FIG. 8  is a flow chart illustrating an example of a power source control process according to each embodiment; 
           [0018]      FIG. 9  is a flow chart illustrating an example of a reference idle period calculation process according to a first embodiment; 
           [0019]      FIG. 10  is a flow chart illustrating an example of a reference idle period calculation process according to a second embodiment; and 
           [0020]      FIG. 11  is a diagram for describing a difference of power source states of an information processing device by the reference idle periods being different. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Examples of embodiments that relate to disclosed techniques will be described below in detail with reference to the drawings. 
         [0022]    First, prior to describing the embodiments in detail, problems in a case where a reference idle period is a fixed value will be described with reference to  FIG. 11 . As described above, the “reference idle period” means a reference period in which a power source is set to an off state in a case of being in an idle state for this period or more. As described above, hereinafter a period that is a shortest value of the period in which the power source of the information processing device is not set to the off state from a time when the power source is set to the on state even if the information processing device is in the idle state, is referred to as a “shortest activated period”. 
         [0023]    As indicated in an upper level in  FIG. 11 , for example, an explanation is made as to a case where 30 minutes of a job execution time, 10 minutes of the idle state period and 20 minutes of the idle state period are repeated in the information processing device. Here, for example, a case where the shortest activated period is 60 minutes is described. The middle level in  FIG. 11  indicates a power source state of the information processing device in a case where the reference idle period is 10 minutes. The lower level in  FIG. 11  indicates a power source state of the information processing device in a case where the reference idle period is 20 minutes. 
         [0024]    In the example indicated in  FIG. 11 , the period in which the power source of the information processing device is in the off state becomes longer in the case where the reference idle period is 20 minutes than in the case where the reference idle period is 10 minutes. Therefore, the amount of power reduction of the information processing device becomes greater. 
         [0025]    In this manner, in a case where the reference idle period is set to a fixed value, there may be a case in which the amount of power consumption of the information processing device is not more reduced than a case in which the reference idle period is set to another value depending on the scheduling circumstances of the job. 
       First Embodiment 
       [0026]    First, a configuration of a power source control system  10  according to the present embodiment will be described with reference to  FIG. 1 . As indicated in  FIG. 1 , the power source control system  10  includes a power source control apparatus  12 , a job management apparatus  14 , and a plurality of nodes  16 . Then, the power source control apparatus  12 , the job management apparatus  14 , and each node  16  are connected to be able to communicate with each other through a network  18 . In the present embodiment, for example, each node  16  is a node that constitutes a comparatively large scale computer system. Parallel processes are executed using each node  16 . 
         [0027]    The power source control apparatus  12  performs control to set the power source in each node  16  to the off state and to the on state. The power source control apparatus  12  will be described later in detail. 
         [0028]    For example, the job management apparatus  14  performs control to cause each node  16  to execute the job by a job scheduler program or the like. Scheduling information  20  which relates to job scheduling and operation record information  22  which relates to past operation recording of a job are stored in a predetermined storage region of the job management apparatus  14 . 
         [0029]      FIG. 2  indicates an example of the scheduling information  20 . As indicated in  FIG. 2 , a job name, a node, a date, a scheduled start time, a scheduled end time, a command, and the like are stored as the scheduling information  20 . 
         [0030]    A name of the job is stored in the job name. A name of the node  16  in which the job is executed is stored in the node. A date at which the job is executed is stored in the date. A scheduled time at which the execution of the job starts is stored in the scheduled start time. A scheduled time at which the execution of the job ends is stored in the scheduled end time. A command that is executed by the job is stored in the command. 
         [0031]      FIG. 3  illustrates an example of the operation record information  22 . As indicated in  FIG. 3 , the job name, the node, the date, a start time, an end time, and the like are stored as the operation record information  22 . 
         [0032]    The name of the job is stored in the job name. The name of the node  16  in which the job is executed is stored in the node. The date at which the job is executed is stored in the date. The time at which the execution of the job starts is stored in the start time. The time at which the execution of the job ends is stored in the end time. 
         [0033]    Next, a functional configuration of the power source control apparatus  12  according to the present embodiment will be described with reference to  FIG. 4 . As indicated in  FIG. 4 , the power source control apparatus  12  includes an acquiring portion  30 , a calculation portion  32 , and a control portion  34 . Standby power information  40  and reference idle period candidate information  42  are stored in a predetermined storage region of the power source control apparatus  12 . 
         [0034]      FIG. 5  indicates an example of the standby power information  40 . As indicated in  FIG. 5 , power consumption [W] in the idle state is stored in each node  16  in the standby power information  40 . As the power consumption, for example, power consumption measured in advance in a state in which the node  16  is in the idle state using a power governor or the like that is provided by Intel (registered trademark) may be stored. 
         [0035]    A plurality of different reference idle period candidates are stored in the reference idle period candidate information  42 . In the present embodiment, for example, a plurality of reference idle periods t i [h] with different arrangement formations such as t i  (i=integers 1 to m)=[0.1, 0.3, . . . ] are stored in the reference idle period candidate information  42 . 
         [0036]    The acquiring portion  30  acquires each of the scheduling information  20  and the operation record information  22  from the job management apparatus  14  via the network  18 . 
         [0037]    The calculation portion  32  calculates a reference idle period t for each node  16  based on the operation record information  22 , the standby power information  40 , and the reference idle period candidate information  42  that are acquired by the acquiring portion  30 . 
         [0038]    First, in the present embodiment, the calculation portion  32  calculates an average interval t in  for each node  16  by analyzing the operation record information  22 , with respect to each reference idle period t i  that is stored in the reference idle period candidate information  42 . The average interval t in  represents an average of intervals in which the idle state of the node  16  continues during the reference idle period t i . 
         [0039]    Specifically, the calculation portion  32  specifies, from the operation record information  22 , a period in which the job is executed and a period in which the job is not executed, that is, a period in which the node  16  is in the idle state. Then, the calculation portion  32  calculates, as the average interval t in , an average value of the intervals of periods that are equal to or more than adjacent reference idle periods t i  out of periods in which the specified node  16  is in the idle state for each reference idle period L. For example, when t i =0.1[h], in a case where it is calculated that t in =0.5[h], the average value of the intervals between the periods in which the idle state of the node  16  continues for 0.1 hours or more is 0.5 hours. 
         [0040]    In addition, the calculation portion  32  calculates an amount of power reduction e[Wh] in a predetermined period L according to the following Formula (1). In Formula (1), I is a minimum value of (shortest activated period T+t i ) or more out of multiples of (t i +t in ). P idle  is power consumption in the idle state of the node  16 . The period L may be set according to an operation policy and the like. The shortest activated period T may be set according to a hardware configuration and the like of the node  16 . 
         [0000]    
       
         
           
             
               
                 
                   e 
                   = 
                   
                     
                       L 
                       l 
                     
                     × 
                     
                       t 
                       i 
                     
                     × 
                     
                       p 
                       idle 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0041]    Then, the calculation portion  32  sets, as the reference idle period t, the reference idle period t i  in which the calculated amount of power reduction e is maximized (that is, the amount of power consumption in the period L is minimized). The calculation portion  32  may set, as the reference idle period t, any reference idle period t i  in which the amount of power reduction e is a predetermined value or more other than the reference idle period t i  in which the amount of power reduction e is maximized. 
         [0042]    Here, for example, a case is described in which it is calculated that t i  (i=1, 2)=[0.1[h], 0.3[h]], t 1n =0.5[h], and t 2n =0.8[h]. Furthermore, for example, a case is described in which T=1[h], L=24[h], and P idle =100[W]. 
         [0043]    In this case, (t 1 +t 1n ) is 0.6[h] and (T+t 1 ) is 1.1[h]. Accordingly, I corresponding to t 1  is 1.2[h]. This means that, as indicated in  FIG. 6 ( 1 ) for example, it is possible to set the power source of the node  16  to the off state during 0.1 hour in every 1.2 hours in a case where the interval between an idle state of 0.1 hour and an idle state of a subsequent 0.1 hour is 0.5 hours in the node  16 .  FIGS. 6 ( 1 ) and  6 ( 2 ) indicate job execution states and power source states of the node  16  that are schematically represented by t i , t in  that are calculated by analyzing the operation record information  22 . The upper level in  FIG. 6 ( 1 ) indicates the job execution state that represents whether the job is being executed or in the idle state (that is, the job is non-executed). The lower level in  FIG. 6 ( 1 ) indicates the power source state that represents whether the power source of the node  16  is in the off state, in the on state in the shortest activated period T, or in the on state after the shortest activated period T has elapsed. 
         [0044]    Then, e corresponding to t 1  is (24/1.2)×0.1×100=200 [Wh] according to Formula (1). 
         [0045]    Meanwhile, (t 2 +t 2n ) is 1.1[h] and (T+t 2 ) is 1.3[h]. Accordingly, I corresponding to t 2  is 2.2[h]. This means that, as indicated in  FIG. 6 ( 2 ) for example, it is possible to set the power source of the node  16  to the off state during 0.3 hours in every 2.2 hours in a case where the interval between an idle state of 0.8 hour and an idle state of a subsequent 0.8 hour is 0.5 hours in the node  16 . The upper level and the lower level in  FIG. 6 ( 2 ) indicate the job execution state and the power source state in the same manner as in  FIG. 6 ( 1 ). 
         [0046]    Then, e corresponding to t 2  is (24/2.2)×0.3×100=327 (Wh) according to Formula (1). 
         [0047]    Accordingly, in this case, the calculation portion  32  calculates the reference idle period t as 0.3[h]. The calculation portion  32  calculates and updates, for each node  16 , the reference idle period t at regular timing such as once a week. Thereby, it is possible to update the reference idle period t to an appropriate value even in a case where there is a change in the scheduling circumstance of the job, the operation policy, and the like. 
         [0048]    The control portion  34  performs control to set the power source of the node  16  to the off state in a case where a period in which the node  16  is in the idle state is equal to or more than the reference idle period t calculated by the calculation portion  32  and the elapsed period from a time when the power source is set to the on state last time exceed the shortest activated period T. For example, the control portion  34  specifies, based on the scheduling information  20 , the timing at which the period in which the node  16  is in the idle state is equal to or more than the reference idle period t and the elapsed period from the time when the power source is set to the on state last time exceed the shortest activated period T. Then, the control portion  34  reserves execution of a process for setting the node  16  to the power off state so that the process is executed at the specified timing. Furthermore, the control portion  34  reserves execution of a process for setting the power source of the node  16  to the on state so that the node  16  is activated and the job can be executed at timing at which the job is executed first after the specified timing. 
         [0049]    For example, the control portion  34  may perform, based on the operation record information  22  and the scheduling information  20 , the process as indicated below in a case where the node  16  is currently in the idle state and the elapsed period from the time when the power source is set to the on state last time exceeds the shortest activated period T. That is, in the above-mentioned case and in a case where the period up to the scheduled start time of the job that is subsequently executed is the reference idle period t or more, the control portion  34  may perform control to set the power source of the node  16  to the off state. Furthermore, in this case, the control portion  34  reserves execution of the process for setting the power source of the node  16  to the on state so that the node  16  is activated and the job can be executed at timing at which the job is executed next. 
         [0050]    For example, the power source control apparatus  12  may be realized by a computer  60  indicated in  FIG. 7 . The computer  60  includes a central processing unit (CPU)  61 , a memory  62  as a temporary storage region, and a nonvolatile storage portion  63 . Furthermore, the computer  60  includes an input and output device  64  such as a display device, an input device, and the like. Furthermore, the computer  60  includes a read/write (R/W) portion  65  that controls reading and writing of data from and to the recording medium  68  and a network I/F  66  that is connected to the network. The CPU  61 , the memory  62 , the storage portion  63 , the input and output device  64 , the R/W portion  65 , and the network I/F  66  are connected to each other via a bus  67 . 
         [0051]    The storage portion  63  may be realized by a hard disk drive (HDD), a solid state device (SSD), a flash memory, and the like. A power source control program  70  for causing the computer  60  to function as the power source control apparatus  12  is stored in the storage portion  63  as the storage medium. The power source control program  70  has an acquisition process  71 , a calculation process  72 , and a control process  73 . The storage portion  63  has an information storage region  74  in which the standby power information  40  and the reference idle period candidate information  42  are stored. 
         [0052]    The CPU  61  reads out the power source control program  70  from the storage portion  63  and develops it in the memory  62 , and executes the processes the power source control program  70  has. The CPU  61  operates as the acquiring portion  30  that is indicated in  FIG. 4  by executing the acquisition process  71 . The CPU  61  operates as the calculation portion  32  that is indicated in  FIG. 4  by executing the calculation process  72 . The CPU  61  operates as the control portion  34  that is indicated in  FIG. 4  by executing the control process  73 . Thereby, the computer  60  that executes the power source control program  70  functions as the power source control apparatus  12 . 
         [0053]    The function realized by the power source control program  70  may also be realized by, for example, a semiconductor integrated circuit, and more specifically an application specific integrated circuit (ASIC) and the like. 
         [0054]    Next, the actions of the power source control apparatus  12  according to the present embodiment will be described. A power source control process indicated in  FIG. 8  is executed by executing the power source control program  70  by the power source control apparatus  12 . For example, the power source control process indicated in  FIG. 8  is executed by the CPU  61  at timing or like at which the power source of the power source control apparatus  12  is set to the on state. 
         [0055]    In step  100  of the power source control process that is indicated in  FIG. 8 , the control portion  34  determines whether or not the update timing of the reference idle period t is arrived at. The process transitions to step  104  in a case where the determination is a negative determination. The process transitions to step  102  in a case where the determination is a positive determination. In the present embodiment, the control portion  34  determines that the update timing of the reference idle period t is arrived at regular timing such as each time one week passes, for example. 
         [0056]    In the subsequent step  102 , the process transitions to step  104  after a reference idle period calculation process that is indicated in  FIG. 9  is executed. 
         [0057]    In step  140  of the reference idle period calculation process that is indicated in  FIG. 9 , the acquiring portion  30  acquires the operation record information  22  from the job management apparatus  14 . The following processes from step  142  to step  154  are executed by setting, as process targets, any node  16  out of all nodes  16 . When the processes from step  142  to step  154  are repeatedly executed, the nodes  16  that have not been set as process targets up to that point are set as the process targets. 
         [0058]    In the subsequent step  142 , the calculation portion  32  assigns 0 to a variable e 0  for holding the maximum value of the amount of power reduction e. The following processes from step  144  to step  152  are repeatedly executed with an initial value of a variable i is 1, and until the variable i exceeds m, that is, repeatedly executed for the same number of times as the number of reference idle periods t i  that is stored in the reference idle period candidate information  42 . 
         [0059]    In step  144 , as described above, the calculation portion  32  calculates the average interval t in  by analyzing the operation record information  22  that is acquired in step  140 . In a subsequent step  146 , as described above, the calculation portion  32  calculates the amount of power reduction e according to Formula (1). In the subsequent step  148 , the calculation portion  32  determines whether or not the amount of power reduction e that is calculated in step  146  is larger than the variable e 0 . The process transitions to step  152  in a case where the determination is a negative determination. The process transitions to step  150  in a case where the determination is a positive determination. 
         [0060]    In step  150 , the calculation portion  32  assigns the value of the variable i to a variable i p  for holding the variable i when the value of the amount of power reduction e that is calculated in step  146  is maximized. The calculation portion  32  assigns the amount of power reduction e that is calculated in step  146  to the variable e 0 . In the subsequent step  152 , the calculation portion  32  increments the variable i. 
         [0061]    In step  154 , the calculation portion  32  sets a reference idle period t ip  that is a number value (value of the variable i p ) of the reference idle period candidate information  42  as the reference idle period t and stores it in the predetermined storage region of the storage portion  63  in association with the node  16  that is the process target. In the subsequent step  156 , the calculation portion  32  determines whether or not the processes from step  142  to step  154  are executed for all nodes  16 . The process returns to step  142  in a case where the determination is a negative determination. The present reference idle period calculation process ends in a case where the determination is a positive determination. When the present reference idle period calculation process ends, the process transitions to step  104  of the power source control process. 
         [0062]    In step  104  that is indicated in  FIG. 8 , the control portion  34  determines whether or not the timing at which the power source state of the node  16  is controlled is arrived at. The process returns to step  100  in a case where the determination is a negative determination. The process transitions to step  106  in a case where the determination is a positive determination. In the present embodiment, the control portion  34  determines at regular timing such as each time three weeks passes, for example that the timing for controlling the power source state of the node  16  is arrived at. 
         [0063]    In step  106 , the acquiring portion  30  acquires the scheduling information  20  from the job management apparatus  14 . The following processes from step  108  to step  118  are executed by setting, as process targets, any node  16  out of all nodes  16 . When the processes from step  108  to step  118  are repeatedly executed, the nodes  16  that have not been set as process targets up to that point are set as the process targets. 
         [0064]    In the subsequent step  108 , the control portion  34  performs the processes indicated below based on the scheduling information  20  that is acquired in step  106 . That is, the control portion  34  specifies a period (hereinafter referred to as “idle state period”) in which the node  16  is in the idle state at the current time or after based on the scheduling information  20 . The following processes from step  110  to step  116  are executed by setting, as process targets, any idle state periods out of all idle state periods that are specified by step  108 . When the processes from step  110  to step  116  are repeatedly executed, the idle state periods that have not been set as process targets up to that point are set as the process targets. 
         [0065]    In step  110 , the control portion  34  determines whether or not the idle state period is the reference idle period t or more that is calculated in step  102 . The process transitions to step  118  in a case where the determination is a negative determination. The process transitions to step  112  in a case where the determination is a positive determination. 
         [0066]    In step  112 , the control portion  34  determines whether or not the elapsed period from a time when the power source of the node  16  is set just before to the on state until the idle state period exceeds the shortest activated period T. The process transitions to step  118  in a case where the determination is a negative determination. The process transitions to step  114  in a case where the determination is a positive determination. 
         [0067]    In step  114 , the control portion  34  reserves execution of a process for setting the power source of the initial node  16  to off state, so that the process is executed at the beginning of the idle state period. 
         [0068]    In the subsequent step  116 , the control portion  34  performs the following processes so that the node  16  is activated and the job can be executed at the timing at which the job is first executed after the timing at which the power source of the node  16  is set to the off state by the process in step  114 . That is, the control portion  34  reserves execution of the process for setting the power source of the node  16  to the on state so that the node  16  is activated and the job can be executed at the timing at which the job is executed first. 
         [0069]    In the subsequent step  118 , the control portion  34  determines whether or not the processes from step  110  to step  116  are completed for all idle state periods that are specified in step  108 . The process returns to step  110  in a case where the determination is a negative determination. The process transitions to step  120  in a case where the determination is a positive determination. 
         [0070]    In the subsequent step  120 , the control portion  34  determines whether or not the processes from step  108  to step  118  are completed for all nodes  16 . The process returns to step  108  in a case where the determination is a negative determination. The process returns to step  100  in a case where the determination is a positive determination. 
         [0071]    As described above, according to the present embodiment, the amount of power reduction e is calculated for each of a plurality of different reference idle times t i  based on the operation record information  22 . Then, control for setting the power source of the node  16  to the off state is performed in a case where the idle state of the node  16  is equal to or more than the reference idle period t at which the amount of power reduction e is maximized. Accordingly, it is possible to reduce the amount of power consumption of the node  16 . 
       Second Embodiment 
       [0072]    Next, a second embodiment will be described. In a power source control system according to the present embodiment, the same parts as in the power source control system  10  according to the first embodiment use the same reference numerals and detailed description is omitted. 
         [0073]    As indicated in  FIG. 1 , a power source control system  210  according to the present embodiment includes a power source control apparatus  212 , the job management apparatus  14 , and the plurality of nodes  16 . 
         [0074]    As indicated in  FIG. 4 , the power source control apparatus  212  according to the present embodiment includes the acquiring portion  30 , a calculation portion  232 , and the control portion  34 . Standby power information  40  and reference idle period candidate information  42  are stored in the predetermined storage region of the power source control apparatus  212 . 
         [0075]    The calculation portion  232  according to the present embodiment calculates the average interval t in  for each of the nodes  16  with respect to each reference idle period t i  that is stored in the reference idle period candidate information  42  in the same manner as the calculation portion  32  according to the first embodiment. 
         [0076]    The calculation portion  232  calculates a function f(t i ) with the idle period t i  as an input and the average interval t in  as an output by performing an interpolation process such as B spline interpolation with each reference idle period t i  and the corresponding average interval t in  as sample points. 
         [0077]    As described above, I in Formula (1) is a minimum value which is (shortest activated period T+t i ) or more out of multiples of (t i +t in ), that is, (t i +f(t i )). Therefore, in the present embodiment, the calculation portion  232  calculates a reference idle period t ib  which becomes minimum when a function h (t ib ) is 0 or more that is indicated by the subsequent Formula (2). 
         [0000]        h ( t   ib )=α×( t   ib   +f ( t   ib ))−( T+t   ib )  (2)
 
         [0078]    In the present embodiment, the calculation portion  232  increases a one by one at 1, 2, 3, . . . , r, and calculates the reference idle period t ib  which becomes minimum when the function h (t ib ) is 0 or more. For example, it is possible to calculate the reference idle period t ib  using an increase and decrease table and the like. The calculation portion  232  calculates the amount of power reduction e for each of the reference idle periods t ib  according to Formula (1). Then, the calculation portion  32  sets, as the reference idle period t, the reference idle period t ib  in which the calculated amount of power reduction e is maximized. An upper limit of a may be appropriately determined according to requested calculation precision and the like. 
         [0079]    The power source control apparatus  12  may be realized by a computer  60  that is indicated in  FIG. 7 , for example. A power source control program  70 A for causing the computer  60  to function as the power source control apparatus  212  is stored in the storage portion  63  of the computer  60 . The power source control program  70 A has the acquisition process  71 , a calculation process  72 A, and the control process  73 . 
         [0080]    The CPU  61  reads out the power source control program  70 A from the storage portion  63  and develops in the memory  62 , and executes a process that the power source control program  70 A has. The CPU  61  operates as the acquiring portion  30  that is indicated in  FIG. 4  by executing the acquisition process  71 . The CPU  61  operates as the calculation portion  232  that is indicated in  FIG. 4  by executing the calculation process  72 A. The CPU  61  operates as the control portion  34  that is indicated in  FIG. 4  by executing the control process  73 . Thereby, the computer  60  that executes the power source control program  70 A functions as the power source control apparatus  212 . 
         [0081]    It is also possible to realize the function realized by the power source control program  70 A by, for example, a semiconductor integrated circuit, and more specifically an ASIC and the like. 
         [0082]    Next, the actions of the power source control apparatus  212  according to the present embodiment will be described. Here, the reference idle period calculation process is described with reference to  FIG. 10  since other than the reference idle period calculation process that is executed in step  102  of the power source control process (refer to  FIG. 8 ), there is no difference from the first embodiment. 
         [0083]    In step  300  of the reference idle period calculation process that is indicated in  FIG. 10 , the acquiring portion  30  acquires the operation record information  22  from the job management apparatus  14 . The following processes from step  302  to step  318  are executed by setting, as process targets, any node  16  out of all nodes  16 . When the processes from step  302  to step  318  are repeatedly executed, the nodes  16  that have not been set as process targets up to that point are set as the process targets. 
         [0084]    In the subsequent step  302 , the calculation portion  232  calculates the average interval t in  for each reference idle period t i  that is stored in the reference idle period candidate information  42  by analyzing the operation record information  22  that is acquired in step  300 . 
         [0085]    In the subsequent step  304 , the calculation portion  232  calculates a function f(t i ) with the reference idle period t i  as an input and the average interval t in  as an output by performing an interpolation process such as B spline interpolation with each reference idle period t i  and the corresponding average interval t in  as sample points. 
         [0086]    In the subsequent step  306 , as described above, the calculation portion  232  calculates the reference idle period t ib  which becomes minimum when the function h(t ib ) is 0 or more according to Formula (2). Here, in order to avoid confusion, it is presumed that p number of reference idle periods t ib  are calculated in the present step  306 . 
         [0087]    In the subsequent step  308 , the calculation portion  232  assigns 0 to a variable e 0  for holding the maximum value of the amount of power reduction e. The following processes from step  310  to step  316  are repeatedly executed until the variable i of which initial value being set to 1 exceeds the p number of reference idle periods t ib  that are calculated in step  306 . 
         [0088]    In step  310 , as described above, the calculation portion  232  calculates the amount of power reduction e according to Formula (1). In the subsequent step  312 , the calculation portion  232  determines whether or not the amount of power reduction e that is calculated in step  310  is larger than the variable e 0 . The process transitions to step  316  in a case where the determination is a negative determination. The process transitions to step  314  in a case where the determination is a positive determination. 
         [0089]    In step  314 , the calculation portion  232  assigns the value of the variable i to a variable i p  for holding the variable i when the amount of power reduction e that is calculated in step  310  is maximized. The calculation portion  232  assigns the amount of power reduction e that is calculated in step  310  to the variable e 0 . In the subsequent step  316 , the calculation portion  232  increments the variable i. 
         [0090]    In step  318 , the calculation portion  232  sets, as the reference idle period t, a reference idle period t ipb  that is a number value (value of the variable i p ) of the reference idle period t ib  that is calculated in step  306  and stores in the predetermined storage region of the storage portion  63  in association with the node  16  that is the process target. In the subsequent step  320 , the calculation portion  232  determines whether or not the following processes from step  302  to step  318  are executed for all nodes  16 . The process returns to step  302  in a case where the determination is a negative determination. The present reference idle period calculation process ends in a case where the determination is a positive determination. When the present reference idle period calculation process ends, the process transitions to step  104  of the power source control process. 
         [0091]    As described above, according to the present embodiment, the reference idle period t is calculated using the function f(t i ) that is obtained by interpolating the average interval that is calculated for each of a plurality of reference idle periods. Accordingly, it is possible to calculate a more appropriate reference idle period t because a reference idle period other than the reference idle period t i  that is stored in the reference idle period candidate information  42  can be a candidate of the reference idle period. 
         [0092]    In the second embodiment, a case where B spline interpolation is applied is described as the interpolation process, but is not limited thereto. For example, as the interpolation process, another interpolation process such as interpolation by a Bezier curve may be applied. 
         [0093]    In each embodiment, an aspect is described in which the power source control programs  70  and  70 A are stored in advance (installed) in the storage portion  63 , but is not limited thereto. It is also possible to provide the power source control programs  70  and  70 A as being stored in a recording medium such as a CD-ROM, a DVD-ROM, a USB memory, or a memory card. 
         [0094]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.