A high-level abstraction of shared accesses

We describe the design and use of the tape mechanism, a new high-level abst raction of accesses to shared data for software DSMs. Tapes consolidate and generalize a number of recent protocol optimizations, including update-bas ed locks and record-replay barriers. Tapes are usually created by "recordin g" shared accesses. The resulting recordings can be used to anticipate futu re accesses by tailoring data movement to application semantics. Tapes-base d mechanisms are layered on top of existing shared-memory protocols, and ar e largely independent of the underlying memory model. Tapes can also be use d to emulate the data-movement semantics of several update-based protocol i mplementations, without altering the underlying protocol implementation. We have used tapes to create the Tapeworm synchronization library. Tapeworm i mplements sophisticated record-replay mechanisms across barriers, augments locks with data-movement semantics, and allows the use of producer-consumer segments, which move entire modified segments when any portion of the segm ent is accessed. We show that Tapeworm eliminates 85% of remote misses, red uces message traffic by 63%, and improves performance by an average of 29% for our application suite.