A method performed by a backfill job scheduler scheduling running of a plurality of jobs (J1-J5) comprised in a set of jobs on a computer system having multiple nodes, wherein each job in the set of jobs requires one or several nodes, the method providing for reducing peak computer system power usage during running of the plurality of jobs, the computer system providing to the scheduler with the capability of controlling processor frequency of operation for one or more selected nodes of the multiple nodes of the computer system, a reduction in node processor frequency typically resulting in reduced power usage on that node during the period of reduced frequency, the steps of the method comprising: a) assigning a first possible schedule executable by the scheduler which specifies a first scheduled order for running the plurality of jobs within a first amount of time; b) modifying the first possible schedule by having the scheduler perform a backfilling operation that produces a second schedule having a second scheduled order for running the plurality of jobs within a scheduled second amount of time, the scheduled second amount of time being less than the first amount of time; c) the scheduler examining the second schedule and identifying holes, wherein a hole is a period of time where no job requires a node, occurring in scheduled time allocated in the second schedule during which one or more individual nodes are not being fully utilized, for creating a list of holes wherein each entry for each hole in the list of holes identifies an underutilized node and an underutilized time period during which the node is not being fully utilized; d) the scheduler further examining or searching the second schedule of step c and identifying those jobs which utilize the underutilized nodes during adjacent time periods in the second schedule, each adjacent time period representing a period of time adjacent in time to each node's associated underutilized periods of time, those jobs being identified or designated as adjacent jobs by the scheduler; and e) the scheduler modifying frequency control parameters included in the second schedule to reduce the frequency of operation of the nodes which are scheduled to run one or more of the identified adjacent jobs during at least a portion of the adjacent time periods and during the associated underutilized periods of time to move processing time of those identified adjacent jobs into the holes in the scheduled time in the second schedule, and to reduce power usage on the node during the adjacent time periods. a) assigning a first possible schedule executable by the scheduler which specifies a first scheduled order for running the plurality of jobs within a first amount of time; b) modifying the first possible schedule by having the scheduler perform a backfilling operation that produces a second schedule having a second scheduled order for running the plurality of jobs within a scheduled second amount of time, the scheduled second amount of time being less than the first amount of time; c) the scheduler examining the second schedule and identifying holes, wherein a hole is a period of time where no job requires a node, occurring in scheduled time allocated in the second schedule during which one or more individual nodes are not being fully utilized, for creating a list of holes wherein each entry for each hole in the list of holes identifies an underutilized node and an underutilized time period during which the node is not being fully utilized; d) the scheduler further examining or searching the second schedule of step c and identifying those jobs which utilize the underutilized nodes during adjacent time periods in the second schedule, each adjacent time period representing a period of time adjacent in time to each node's associated underutilized periods of time, those jobs being identified or designated as adjacent jobs by the scheduler; and e) the scheduler modifying frequency control parameters included in the second schedule to reduce the frequency of operation of the nodes which are scheduled to run one or more of the identified adjacent jobs during at least a portion of the adjacent time periods and during the associated underutilized periods of time to move processing time of those identified adjacent jobs into the holes in the scheduled time in the second schedule, and to reduce power usage on the node during the adjacent time periods.