1. A computer implemented method for marking instructions for instrumentation, the computer implemented method comprising: presenting a plurality of instructions in a graphical user interface; receiving through the graphical user interface, a user input selecting a set of instructions in the plurality of instructions for instrumentation, wherein the plurality of instructions include instrumentation instructions and non-instrumentation instructions; providing a register in a processor, wherein the register includes a target field and a mode field, wherein an identification of a target processor that will be used to execute the selected set of instructions when the target processor is in an instrumentation mode is specified in the target field and a flag that is set in the mode field, wherein the flag indicates whether the target processor is in the instrumentation mode; receiving, by the graphical user interface while the processor is executing, the identification of the target processor; receiving, by the graphical user interface while the processor is executing, a value for the responsive to receiving the user input, marking the set of instructions as instrumentation instructions a set of instrumentation instructions, wherein the set of instructions are executed by the target processor identified by the identification when the value indicates that the target processor is in the instrumentation mode; and wherein the set of instrumentation instructions are skipped and not executed if the flag indicates that the target processor is not in the instrumentation mode.