1.  Introduction

      The Berkeley Software Distributions of UNIXfor the VAX have added many new capabilities that were previously unavailable under UNIXThe development effort for 4.2BSD concentrated on providing new facilities, and in getting them to work correctly. Many new data structures were added to the system to support these new capabilities. In addition, many of the existing data structures and algorithms were put to new uses or their old functions placed under increased demand. The effect of these changes was that mechanisms that were well tuned under 4.1BSD no longer provided adequate performance for 4.2BSD. The increased user feedback that came with the release of 4.2BSD and a growing body of experience with the system highlighted the performance shortcomings of 4.2BSD.

      This paper details the work that we have done since the release of 4.2BSD to measure the performance of the system, detect the bottlenecks, and find solutions to remedy them. Most of our tuning has been in the context of the real timesharing systems in our environment. Rather than using simulated workloads, we have sought to analyze our tuning efforts under realistic conditions. Much of the work has been done in the machine independent parts of the system, hence these improvements could be applied to other variants of UNIX with equal success. All of the changes made have been included in 4.3BSD.

      Section 2 of the paper describes the tools and techniques available to us for measuring system performance. In Section 3 we present the results of using these tools, while Section 4 has the performance improvements that have been made to the system based on our measurements. Section 5 highlights the functional enhancements that have been made to Berkeley UNIX 4.2BSD. Section 6 discusses some of the security problems that have been addressed.