Measuring and Improving the Performance

The 4.2 Berkeley Software Distribution of UNIX® for the VAX‡ had several problems that could severely affect the overall performance of the system. These problems were identified with kernel profiling and system tracing during day to day use. Once potential problem areas had been identified benchmark programs were devised to highlight the bottlenecks. These benchmarks verified that the problems existed and provided a metric against which to validate proposed solutions. This paper examines the performance problems encountered and describes modifications that have been made to the system since the initial distribution. The changes to the system have consisted of improvements to the performance of the existing facilities, as well as enhancements to the current facilities. Performance improvements in the kernel include cacheing of path name translations, reductions in clock handling and scheduling overhead, and improved throughput of the network subsystem. Performance improvements in the libraries and utilities include replacement of linear searches of system databases with indexed lookup, merging of most network services into a single daemon, and conversion of system utilities to use the more efficient facilities available in 4.2BSD. Enhancements in the kernel include the addition of subnets and gateways, increases in many kernel limits, cleanup of the signal and autoconfiguration implementations, and support for windows and system logging. Functional extensions in the libraries and utilities include the addition of an Internet name server, new system management tools, and extensions to dbx to work with Pascal. The paper concludes with a brief discussion of changes made to the system to enhance security. All of these enhancements are present in Berkeley UNIX 4.3BSD. CR