File Access Performance of Diskless Workstations

This paper studies the performance of single-user workstations that access files remotely over a local area network. From the environmental, economic, and administrative points of view, workstations that are diskless or that have limited secondary storage are desirable at the present time. Even with changing technology, access to shared data will continue to be important. It is likely that some performance penalty must be paid for remote rather than local file access. Our objectives are to assess this penalty and to explore a number of design alternatives that can serve to minimize it. Our approach is to use the results of measurement experiments to parameterize queuing network performance models. These models then are used to assess performance under load and to evahrate design alternatives. The major conclusions of our study are: (1) A system of diskless workstations with a shared file server can have satisfactory performance. By this, we mean performance comparable to that of a local disk in the lightly loaded case, and the ability to support substantial numbers of client workstations without significant degradation. As with any shared facility, good design is necessary to minimize queuing delays under high load. (2) The key to efficiency is protocols that allow volume transfers at every interface (e.g., between client and server, and between disk and memory at the server) and at every level (e.g., between client and server at the level of logical request/response and at the level of local area network packet size). However, the benefits of volume transfers are limited to moderate sizes (8-16 kbytes) by several factors. (3) From a performance point of view, augmenting the capabilities of the shared file server may be more cost effective than augmenting the capabilities of the client workstations. (4) Network contention should not be a performance problem for a lo-Mbit network and 100 active workstations in a software development environment

Improving Cache Performance by Eliminating Transfers of Dead Data

Traditional main memory caches provide semantics that deal with memory locations rather than the data they contain. By considering the cache as a repository of data, rather than locations, it is possible to eliminate transfers associated with dead data, data that is guaranteed not to be referenced again. The transfers eliminated correspond to fetches of cache lines that will be completely overwritten without being read, and to writebacks of data that will never again be read. We describe the semantics and implementation of a set of cache control instructions that, when added to a conventional instruction set, allow the elimination of dead data transfers. We demonstrate how these instructions could be employed by a compiler, and give a quantitative assessment of their benefits. This assessment is based on trace-driven cache simulations of benchmarks from the Livermore Loops, SPEC, and Perfect Club suites. As part of this study, we determine the maximum benefit attainable through the use..