Mode switching in dependence upon a number of active threads

Apparatus for processing data comprising:

• means for fetching program instructions for execution from one or more active threads of program instructions having respective program counter values;
• means for executing program instructions fetched by said means for fetching, said means for executing having a first operating mode and a second operating mode;
• and
• means for switching said means for executing between said first operating mode and said second operating mode in dependence upon a number of active threads of program instructions having program instructions fetched by said means for fetching and available to be executed by said means for executing,
• means for predicting branch instruction outcomes, wherein said means for predicting has a first branch prediction mode corresponding to said first operating mode of said means for executing and a second branch prediction mode corresponding to said second operating mode of said means for executing, said first branch prediction mode consuming less power and providing less accurate branch predictions than said second branch prediction mode which consumes more power and provides more accurate branch predictions, wherein:
• said first operating mode has a lower average energy consumption per instruction executed than said second operating mode, said second operating mode has a higher average rate of instruction execution for a single thread than said first operating mode, and at least one portion of said means for executing is disabled in one of said first operating mode and said second operating mode and enabled in a different one of said first operating mode and said second operating mode;
• said means for executing comprises out-of-order processing circuitry supporting out-of-order program instruction execution, and
• operation of said out-of-order processing circuitry corresponding to said second operating mode and said second branch prediction mode.

A method of processing data, comprising:

• fetching program instructions for execution from one or more active threads of program instructions having respective program counter values;
• executing program instructions fetched by said fetching, said program instructions being executable in a first operating mode and a second operating mode;
• and
• switching between said first operating mode and said second operating mode in dependence upon a number of active threads of program instructions having program instructions fetched by said fetching and available to be executed;
• and
• predicting branch instruction outcomes, wherein a first branch prediction mode corresponds to said first operating mode and a second branch prediction mode corresponds to said second operating mode, said first branch prediction mode consumes less power and provides less accurate branch predictions than said second branch prediction mode which consumes more power and provides more accurate branch predictions, wherein
• said first operating mode has a lower average energy consumption per instruction executed than said second operating mode, said second operating mode has a higher average rate of instruction execution for a single thread than said first operating mode, and at least one portion of circuitry to execute said program instructions is disabled in one of said first operating mode and said second operating mode and enabled in a different one of said first operating mode and said second operating mode;
• and
• said executing program instructions comprise executing out-of-order program instructions, said executing out-of-order processing program instructions corresponding to said second operating mode and said second branch prediction mode.