Reducing the associativity and size of step caches in CRCW operation

Step caches are caches in which data entered to an cache array is kept valid only until the end of ongoing step of execution. Together with an advanced pipelined multithreaded architecture they can be used to implement concurrent read concurrent write (CRCW) memory access in shared memory multiprocessor systems on chip (MP-SOC) without cache coherency problems. Unfortunately obvious step cache architectures assume full associativity, which can become expensive since the size and thus associativity of caches equal the number of threads per processor being at least the square root of the number of processors. In this paper, we describe a technique to radically reduce the associativity and even size of step caches in CRCW operation. We give a short performance evaluation of limited associativity step cache systems with different settings using simple parallel programs on a parametrical MP-SOC framework. According to the evaluation, the performance of limited associativity step cache systems comes very close to that of fully associative step cache systems, while decreasing the size of caches decreases the performance gradually.