A flexible cache coherency protocol for the Ruby memory system

Gem5’s Ruby memory subsystem provides flexible on-chip network models and multiple cache coherency protocols modeled in detail. However, simple experiments are sometimes difficult to pull off. For instance, modifying an existing configuration by just adding another shared cache level requires either:

  1. switching to an entirely new protocol that models the desired cache hierarchy;
  2. or modify an existing protocol;

While (1) is not always an option, (2) is a non-trivial task since Ruby protocols can be very complex and hard to debug. This creates a major flexibility gap between gem5 “classic” memory sub-system and Ruby.

New protocol implementation

We are working on a new protocol implementation that aims at addressing this configurability limitation. Our new protocol provides a single cache controller that can be reused at multiple levels of the cache hierarchy and configured to model multiple instances of MESI and MOESI cache coherency protocols. This implementation is based of Arm’s AMBA 5 CHI specification and provides a scalable framework for the design space exploration of large SoC designs.


To known more please take a look at our workshop presentation: