A method comprising: on a graphics, GFX, core comprising a plurality of Subslices (14; 14'), executing a workload in a first mode wherein each of the plurality of Subslices receives power for at least a number of clock cycles and wherein each of the plurality of Subslices operates in a power down state for at least another number of clock cycles, wherein in the power down state each of the plurality of Subslices is idle; calculating a number of clock cycles, Tfirst mode, required for the GFX core to perform the workload in the first mode during a first decision window comprising a plurality of clock cycles; calculating a number of clock cycles, Tsecond mode, required for the GFX core to perform the workload in a second mode during the first decision window wherein the second mode comprises executing the workload with fewer of the plurality of Subslices receiving power than when executing the workload in the first mode; determining if the GFX core operated in a power down state during the first decision window; determining, based in part upon Tfirst mode and Tsecond mode, if an energy savings is possible by transitioning the GFX core to the second mode if it is determined that the GFX core operated in a power down state during the first decision window; and transitioning the GFX core to the second mode, subsequent to executing the workload, if it is determined that an energy savings is possible by transitioning the GFX core to the second mode; executing a workload on the graphics, GFX, core in the second mode; calculating a percentage of time that the GFX core operated in a power down state during a second decision window comprising a plurality of clock cycles; determining if the percentage exceeds a predefined threshold; determining, if the percentage exceeds a predefined threshold, if the percentage of time that the GFX core operated in the power down state during the second decision window is attributable to a periodic activity pattern; and transitioning the GFX core to the first mode if it is determined that at least a portion of the percentage of time that the GFX core operated in the power down state during the second decision window is not attributable to the periodic activity pattern. on a graphics, GFX, core comprising a plurality of Subslices (14; 14'), executing a workload in a first mode wherein each of the plurality of Subslices receives power for at least a number of clock cycles and wherein each of the plurality of Subslices operates in a power down state for at least another number of clock cycles, wherein in the power down state each of the plurality of Subslices is idle; calculating a number of clock cycles, Tfirst mode, required for the GFX core to perform the workload in the first mode during a first decision window comprising a plurality of clock cycles; calculating a number of clock cycles, Tsecond mode, required for the GFX core to perform the workload in a second mode during the first decision window wherein the second mode comprises executing the workload with fewer of the plurality of Subslices receiving power than when executing the workload in the first mode; determining if the GFX core operated in a power down state during the first decision window; determining, based in part upon Tfirst mode and Tsecond mode, if an energy savings is possible by transitioning the GFX core to the second mode if it is determined that the GFX core operated in a power down state during the first decision window; and transitioning the GFX core to the second mode, subsequent to executing the workload, if it is determined that an energy savings is possible by transitioning the GFX core to the second mode; executing a workload on the graphics, GFX, core in the second mode; calculating a percentage of time that the GFX core operated in a power down state during a second decision window comprising a plurality of clock cycles; determining if the percentage exceeds a predefined threshold; determining, if the percentage exceeds a predefined threshold, if the percentage of time that the GFX core operated in the power down state during the second decision window is attributable to a periodic activity pattern; and transitioning the GFX core to the first mode if it is determined that at least a portion of the percentage of time that the GFX core operated in the power down state during the second decision window is not attributable to the periodic activity pattern.