ACID Support for Compute eXpress Link Memory Transactions

With the recent explosive growth in worldwide data and data processing demands, the need to support a large volume of transactions on shared data is increasing in both high performance computing and datacenter processing. A recent innovation in server architectures is the use of disaggregated memory based on the Compute eXpress Link (CXL) interconnect protocol. This memory architecture is increasing in popularity as it allows for dynamic demand-sensitive resizing of aggregated memory, support for heterogeneous memory types, and sharing of data amongst supported processors and devices, including computational accelerators. However, while this new memory architecture alleviates many concerns in datacenter architectures, the data integrity when using memory based transactions over CXL faces many challenges.To solve for these challenges, we describe a novel solution for providing ACID (Atomicity, Consistency, Isolation, Durability) transactions in a CXL-based disaggregated memory architecture. We call this solution Transactional CXL or TCXL. TCXL requires no changes to the existing processor microarchitectures and is implemented in a software library with a back-end controller that can be embedded in a CXL controller or as a stand alone CXL Device or implemented on a host.The transactions support persistent memory durable transactions and in-memory volatile transactions which can be in a pooled memory expansion for a single processor or shared amongst multiple processors. TCXL also supports processor based Hardware Transactional Memory (HTM) based transactions both on processor and over CXL. We evaluate TCXL by extending a CXL simulator and executing micro-benchmarks. In addition to gaining the benefits of using CXL, we show TCXL outperforms other approaches.