Improving IPC by Kernel

Inter-process communication (ipc) has to be fast and eeective, otherwise programmers will not use remote procedure calls (RPC), multithreading and multitasking adequately. Thus ipc performance is vital for modern operating systems, especially-kernel based ones. Surprisingly , most-kernels exhibit poor ipc performance, typically requiring 100 s for a short message transfer on a modern processor, running with 50 MHz clock rate. In contrast, we achieve 5 s; a twentyfold improvement. This paper describes the methods and principles used, starting from the architectural design and going down to the coding level. There is no single trick to obtaining this high performance; rather, a synergetic approach in design and implementation on all levels is needed. The methods and their synergy are illustrated by applying them to a concrete example, the L3-kernel (an industrial-quality operating system in daily use at several hundred sites). The main ideas are to guide the complete kernel design by the ipc requirements, and to make heavy use of the concept of virtual address space inside the-kernel itself. As the L3 experiment shows, signiicant performance gains are possible: compared with Mach, they range from a factor of 22 (8-byte messages) to 3 (4-Kbyte messages). Although hardware speciic details innuence both the design and implementation, these techniques are applicable to the whole class of conventional general 0 Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or speciic permission. purpose von Neumann processors supporting virtual addresses. Furthermore, the eeort required is reasonably small, for example the dedicated parts of the-kernel can be concentrated in a single medium sized module. 1 The IPC Dilemma Inter-process communication (ipc) by message passing is one of the central paradigms of most-kernel based and other client/server architectures. It helps to increase modularity, exibility, security and scalability, and it is the key for distributed systems and applications. To gain acceptance by programmers and users, ipc has to become a very eecient basic mechanism. Surprisingly , most ipc implementations perform poorly. Dependent on the processor speed, transferring a short message by ipc typically takes between 50 and 500 s. A lot of eeort …