Named State and Efficient Context Switching

Abstract

Context switches are slow in conventional processors becausethe entire processor state must be saved and restored, even if much ofthe restored state is not used before the next context switch. Thisunnecessary data movement is required because of the coarse granularityof binding between names and registers. In this paper we introduce theContext Cache, which binds variable names to individual registers. Thisallows context switches to be very inexpensive, since registers are onlyloaded and saved out as needed. Analysis shows that the Context Cacheuses registers more efficiently than a multithreaded register file, andsupports more tasks without spilling to memory. Circuit simulationsindicated that the access time of a Context Cache only requires 25%more VLSI chip area to implement than a conventional register file.