Removing the Overhead from Software-Based Shared Memory

The implementation presented in this paper — DSZOOM-WF — is a sequentially consistent, fine-grained distributed software-based shared memory. It demonstrates a protocol-handling overhead below a microsecond for all the actions involved in a remote load operation, to be compared to the fastest implementation to date of around ten microseconds. The all-software protocol is implemented assuming some basic low-level primitives in the cluster interconnect and an operating system bypass functionality, similar to the emerging InfiniBand standard. All interrupt- and/or poll-based asynchronous protocol processing is completely removed by running the entire coherence protocol in the requesting processor. This not only removes the asynchronous overhead, but also makes use of a processor that otherwise would stall. The technique is applicable to both page-based and fine-grain software-based shared memory. DSZOOM-WF consistently demonstrates performance comparable to hardware-based distributed shared memory implementations.