Methods and apparatus for context switching

An apparatus comprising:

• execution circuitry comprising at least one execution unit to execute program instructions;
• and
• control circuitry configured to:
• receive a stream of processing instructions of an initial context;
• and
• issue each received instruction to one of said at least one execution unit,
• responsive to determining that a first type of context switch is to be performed from the initial context to a new context:
• continue issuing received instructions until a pre-emption point in the stream of processing instructions is reached;
• and
• responsive to reaching the pre-emption point:
• store state information associated with a current status of processing the stream of processing instructions;
• and
• switch to the new context, and
• responsive to determining that a further context switch is to be performed to return from the new context to the initial context:
• restore the processing status from the state information;
• and
• continue issuing the stream of processing instructions, wherein the control circuitry is:
• responsive to determining that a second type of context switch is to be performed from the initial context to the new context to:
• abort the issuing of the stream of processing instructions;
• and
• switch to the new context,
• responsive to determining that the further context switch is to be performed subsequent to the second type of context switch to return from the new context to the initial context:
• to begin issuing the stream of processing instructions, starting at an instruction corresponding to a safe restart point, wherein the safe restart point is a point from which the stream of processing instructions can be safely restarted;
• and
• configured to determine whether to perform the first type of context switch or the second type of context switch based on a magnitude of a difference between priority values of the initial context and the new context.