A mechanism for efficient context switching

Abstract

Context switches are slow in conventional processors because the entire processor state must be saved and restored, even if much of the restored state is not used before the next context switch. This unnecessary data movement is required because of the coarse granularity of binding between names and registers. The context cache is introduced, which binds variable names to individual registers. This allows context switches to be very inexpensive, since registers are only loaded and saved out as needed. Analysis shows that the context cache holds more live data than a multithreaded register file, and supports more tasks without spilling to memory. Circuit simulations show that the access time of a context cache is 7% greater than a conventional register file of the same size.<>