The case for simple, visible cache coherency

The shared memory research community has proposed many complex communication protocols that aim to eliminate specific performance bottlenecks, while still providing an easy-to-use communication interface. Although tailored protocols can eliminate some bottlenecks that arise in real applications, removing the cause of the bottleneck through software optimizations and bug fixes is cheaper to implement, faster to fix (once found), and requires no additional support by the hardware beyond a simple shared memory interface. In fact, in our experience, the choice of coherence protocol is much less important than providing an efficient hardware feedback that indentifies the source of the problem. Future cache-coherence research should focus efforts on illuminating memory system behavior, providing smarter tools to identify bottlenecks, and helping to eliminate them through software optimizations.