Effects of re-ordered memory operations on parallelism
Richard H. Littin, John G. Cleary · 1997
The performance effect of permitting different memory operations to be re-ordered is examined. The available parallelism is computed using a machine code simulator. A range of possible restrictions on the re-ordering of memory operations is considered: from the purely sequential case where no re-ordering is permitted; to the completely permissive one where memory operations may occur in any order so that the parallelism is restricted only by data dependencies. A general conclusion is drawn that to reliably obtain parallelism beyond 10 instructions per clock will require an ability to re-order all memory instructions. A brief description of a feasible architecture capable of this is given. Keywords: memory access, parallelism, out-of-order execution. 1 Introduction Today's computer architectures make use of out-of-order instruction execution to extract parallelism (and performance) out of the code they run. This dynamic execution is achieved through the use of reservation stations [To...