Kenneth Mackenzie, John Kubiatowicz, Anant Agarwal and M. Frans Kaashoek. FUGU: Implementing Translation and Protection in a Multiuser, Multimodel Multiprocessor. Technical Memo MIT/LCS/TM-503, October, 1994.
(postscript file)

Abstract:

Multimodel multiprocessors provide both shared memory and message passing primitives to the user for efficient communication. In a multiuser machine, translation permits machine resources to be virtualized and protection permits users to be isolated. The challenge in a multiuser multiprocessor is to provide translation and protection sufficient for general-purpose computing without compromising communication performance, particularly the performance of communication between parallel threads belonging to the same computation. FUGU is a proposed architecture that integrates translation and protection with a set of communication mechanisms originally designed for high performance on a single-user, physically-addressed, large-scale, multimodel multiprocessor.

Communication in FUGU is based on the mechanisms of the Alewife machine. The mechanisms are shared memory with hardware cache coherence, user-level message sends and receives, and a user-controlled DMA facility integrated with messages for bulk transfers. This paper presents a design that integrates translation and protection with these communication mechanisms. Three components of the design are novel. First, we propose maintaining TLB coherence as a side-effect of cache coherence on page table entries. Second, we describe how to permit user-launched and user-handled messages without dedicating physical memory for buffering at the sender or at the receiver. We propose to use a rudimentary, second, system-only network to avoid deadlock of the user-accessible network. Third, we show how to integrate user DMA with virtual memory to permit bulk transfers without prenegotiation and global locking of physical memory.