Fresh Breeze

Abstract

It is well-known that multiprocessor systems are vastly more difficult to program than systems that support sequential programming models. In a 1998 paper[11] this author argued that six important principles for supporting modular software construction are often violated by the architectures proposed for multiprocessor computer systems. The Fresh Breeze project concerns the architecture and design of a multiprocessor chip that can achieve superior performance while honoring these six principles.The envisioned multiprocessor chip will incorporate three ideas that are significant departures from mainstream thinking about multiprocessor architecture: (1) Simultaneous multithreading has been shown to have performance advantages relative to contemporary superscalar designs. This advantage can be exploited through use of a programming model that exposes parallelism in the form of multiple threads of computation. (2) The value of a shared address space is widely appreciated. Through the use of 64-bit pointers, the conventional distinction between "memory" and the file system can be abolished. This can provide a superior execution environment in support of program modularity and software reuse, as well as supporting multi-user data protection and security that is consistent with modular software structure. (3) No memory update; cycle-free heap. Data items are created, used, and released, but never modified once created. The allocation, release, and garbage collection of fixed-size chunks of memory will be implemented by efficient hardware mechanisms. A major benefit of this choice is that the multiprocessor cache coherence problem vanishes: any object retrieved from the memory system is immutable. In addition, it is easy to prevent the formation of pointer cycles, simplifying the design of memory management support.