Support for multimedia applications by general purpose computing platforms has been the subject of considerable research. Much of this work is based on an evolutionary strategy in which small changes to existing systems are made. The approach adopted here is to start ab initio with no backward compatibility constraints. This leads to a novel structure for an operating system. The structure aims to decouple applications from one another and to provide multiplexing of all resources, not just the CPU, at a low level. The motivation for this structure, a design based on the structure, and its implementation on a number of hardware platforms is described. I. Introduction G ENERAL purpose multimedia computing platforms should endow text, images, audio and video with equal status: interpreting an audio or video stream should not be a privileged task of special functions provided by the operating system, but one of ordinary user programs. Support for such processing on a platform on which ot...

The explosive growth of the Internet, the widespread use of WWW-related applications, and the increased reliance on client-server architectures places interesting new demands on network servers. In particular, the operating system running on such systems needs to manage the machine’s resources in a manner that maximizes and maintains throughput under conditions of high load. We propose and evaluate a new network subsystem architecture that provides improved fairness, stability, and increased throughput under high network load. The architecture is hardware independent and does not degrade network latency or bandwidth under normal load conditions.

Fast and flexible message demultiplexing are well-established goals in the networking community [1, 18, 22]. Currently, however, network architects have had to sacrifice one for the other. We present a new packet-filter system, DPF (Dynamic Packet Filters), that provides both the traditional flexibility of packet filters [18] and the speed of hand-crafted demultiplexing routines [3]. DPF filters run 10--50 times faster than the fastest packet filters reported in the literature [1, 17, 18, 27]. DPF's performance is either equivalent to or, when it can exploit runtime information, superior to handcoded demultiplexors. DPF achieves high performance by using a carefully-designed declarative packet-filter language that is aggressively optimized using dynamic code generation. The contributions of this work are: (1) a detailed description of the DPF design, (2) discussion of the use of dynamic code generation and quantitative results on its performance impact, (3) quantitative results on how ...

Application-specific safe message handlers (ASHs) are designed to provide applications with hardware-level network performance. ASHs are user-written code fragments that safely and efficiently execute in the kernel in response to message arrival. ASHs can direct message transfers (thereby eliminating copies) and send messages (thereby reducing send-response latency). In addition, the ASH system provides support for dynamic integrated layer processing (thereby eliminating duplicate message traversals) and dynamic protocol composition (thereby supporting modularity). ASHs provide this high degree of flexibility while still providing network performance as good as, or (if they exploit application-specific knowledge) even better than, hard-wired in-kernel implementations. A combination of user-level microbenchmarks and end-to-end system measurements using TCP demonstrate the benefits of the ASH system.

We are building a very high performance 1.2 Gb/s ATM network interface chip called the APIC (ATM Port Interconnect Controller). In addition to borrowing useful ideas from a number of research and commercial prototypes, the APIC design embraces several innovative features, and integrates all of these pieces into a coherent whole. This paper describes some of the novel ideas that have been incorporated in the APIC design with a view to improving the bandwidth and latency seen by end-applications. Among the techniques described, Protected DMA and Protected I/O were designed to allow applications to queue data for transmission or reception directly from user-space, effectively bypassing the kernel. This argues for moving the entire protocol stack including the interface device driver into user-space, thereby yielding better latency and throughput performance than kernel-resident implementations. Pool DMA when used with Packet Splitting, is a technique that can be used to build true zero-co...

This paper presents a novel networking architecture designed for communication intensive parallel applications running on clusters of workstations (COWs) connected by high speed networks. This architecture permits (1) the transfer of selected communication-related functionality from the host machine to the network interface coprocessor, and (2) the exposure of this functionality directly to applications as instructions of aVirtual Communication Machine (VCM) implemented by the coprocessor. The user-level code interacts directly with the network coprocessor as the host kernel only 'connects' the application to the VCM and does not participate in the data transfers. The distinctive feature of our design is its flexibility: the integration of the network withthe applicationcan be varied to maximize performance. The resulting communication architecture is characterized by a very low overhead on the host processor, by latency and bandwidth close to the hardware limits, and by an applicatio...

Data copying and checksumming are the most expensive operations when doing high-bandwidth network IO over a highspeed network. Under some conditions, outboard buffering and checksumming can eliminate accesses to the data, thus making communication less expensive and faster. One of the scenarios in which outboard buffering pays off is the common case of applications accessing the network using the Berkeley sockets interface and the Internet protocol stack. In this paper we describe the changes that were made to a BSD protocol stack to make use of a network adaptor that supports outboard buffering and checksumming. Our goal is not only to achieve "single copy" communication for application that use sockets, but to also have efficient communication for in-kernel applications and for applications using other networks. Performance measurements show that for large reads and writes the single-copy path through the stack is significantly more efficient than the original implementation. 1 Intr...

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FFPF is a network monitoring framework designed for three things: speed (handling high link rates), scalability (ability to handle multiple applications) and flexibility. Multiple applications that need to access overlapping sets of packets may share their packet buffers, thus avoiding a packet copy to each individual application that needs it. In addition, context switching and copies across the kernel boundary are minimised by handling most processing in the kernel or on the network card and by memory mapping all buffers to userspace, respectively. For these reasons, FFPF has superior performance compared to existing approaches such as BSD packet filters, and especially shines when multiple monitoring applications execute simultaneously. Flexibility is achieved by allowing expressions written in different languages to be connected to form complex processing graphs (not unlike UNIX processes can be connected to create complex behaviour using pipes). Moreover, FFPF explicitly supports extensibility by allowing new functionality to be loaded at runtime. By also implementing the popularpcap packet capture library on FFPF, we have ensured backward compatibility with many existing tools, while at the same time giving the applications a signficant performance boost. 1

This dissertation considers various problems associated with the scheduling and network I/O organisation found in conventional operating systems for effective support for multimedia applications which require Quality of Service. A solution for these problems is proposed in a micro-kernel structure. The pivotal features of the proposed design are that the processing of device interrupts is performed by user-space processes which are scheduled by the system like any other, that events are used for both inter- and intra- process synchronisation, and the use of a specially developed high performance I/O buffer management system. An evaluation of an experimental implementation is included. In addition to solving the scheduling and networking problems addressed, the prototype is shown to out-perform the Wanda system (a locally developed micro-kernel) on the same platform. This dissertation concludes that it is possible to construct an operating system where the kernel provides only the fu...