We have designed and implemented a new operating system facility for I/O buffer management and data transfer across protection domain boundaries on shared memory machines. This facility, called fast buffers (fbufs), combines virtual page remapping with shared virtual memory, and exploits locality in I/O traffic to achieve high throughput withoutcompromising protection, security, or modularity. Its goal is to help deliver the high bandwidth afforded by emerging high-speed networks to user-level processes, both in monolithic and microkernel-based operating systems. This paper outlines the requirements for a cross-domain transfer facility, describes the design of the fbuf mechanism that meets these requirements, and experimentally quantifies the impact of fbufs on network performance. 1 Introduction Optimizing operations that cross protection domain boundaries has received a great deal of attention recently [2, 3]. This is because an efficient cross-domain invocation facility enables a ...

Mach is a multiprocessor operating system kernel and environment under development at Carnegie Mellon University. Mach provides a new foundation for UNIX development that spans networks of uniprocessors and multiprocessors. This paper describes Mach and the motivations that led to its design. Also described are some of the details of its implementation and current status. 1

Consistent checkpointing provides transparent fault tolerance for long-running distributed applications. In this paper we describe performance measurements of an implementation of consistent checkpointing. Our measurements show that consistent checkpointing performs remarkably well. We executed eight compute-intensive distributed applications on a network of 16 diskless Sun-3/60 workstations, comparing the performance without checkpointing to the performance with consistent checkpoints taken at 2-minute intervals. For six of the eight applications, the running time increased by less than 1% as a result of the checkpointing. The highest overhead measured for any of the applications was 5.8%. Incremental checkpointing and copy-on-write checkpointing were the most effective techniques in lowering the running time overhead. These techniques reduce the amount of data written to stable storage and allow the checkpoint to proceed concurrently with the execution of the processes. The overhead ...

Memory Management Units (MMUs) are traditionally used by operating systems to implement disk-paged virtual memory. Some operating systems allow user programs to specify the protection level (inaccessible, readonly. read-write) of pages, and allow user programs t.o handle protection violations. bur. these mechanisms are not. always robust, efficient, or well-mat. ched to the needs of applications.

This paper describes a new feature in Solaris that uses virtual memory remapping combined with checksumming support from the networking hardware, to eliminate data-touching overhead from the TCP/IP protocol stack. By implementing page remapping operations at the right level of the operating system, and caching MMU mappings to take advantage of locality of reference, significant performance gain is attained on certain hardware platforms. Nevertheless, the performance improvement over CPU copying varies, depending on the host memory cache architecture, MMU design, and application behavior. We begin by comparing different zero-copy schemes, and explain our preference for page remapping and copy-on-write (COW) techniques. We then describe our implementation, and present its performance characteristics under a number of different parameters. We conclude with ideas for future improvements. 1. Introduction High data throughput is one of the major requirements for applications such as multim...

Traditional UNIX ® I/O interfaces are based on copy semantics, where read and write calls transfer data between the kernel and user-defined buffers. Although simple, copy semantics limit the ability of the operating system to efficiently implement data transfer operations. In this paper, we present extensions on the traditional UNIX interfaces that are based on explicit buffer exchange. Instead of transferring data between user-defined buffers and the kernel, the new extensions transfer data buffers between the user and the kernel. We study using the new interfaces in typical application programs, and compare their use to the standard UNIX interfaces. The new interfaces lend themselves to an efficient zero-copy data transfer implementation. We describe such an implementation in this paper, and we examine its performance. The implementation, done in the context of the Solaris TM operating system, is very efficient: for example, on a typical file transfer benchmark, the network throughput was improved by more than 40 % and the CPU utilization reduced by more than 20%.

This paper describes the design and evaluates the performance of the DASH MP system, with an emphasis on its use of remapping. In addition, we study the system performance at a `microscopic' level by breaking down a user-level MP operation into short segments and measuring their individual performance. The results are used to evaluate and refine our design decisions

Certain applications, such as Windows 2000’s Remote Install service, can result in a set of files in which many different files have the same content. Using a traditional file system to store these files separately results in excessive use of disk and main memory file cache space. Using hard or symbolic links would eliminate the excess resource requirements, but changes the semantics of having separate files, in that updates to one “copy ” of a file would be visible to users of another “copy. ” We describe the Single Instance Store (SIS), a component within Windows ® 2000 that implements links with the semantics of copies for files stored on a Windows 2000 NTFS volume. SIS uses copy-on-close to implement the copy semantics of its links. SIS is structured as a file system filter driver that implements links and a user level service that detects duplicate files and reports them to the filter for conversion into links. Because SIS links are semantically identical to separate files, SIS creates them automatically when it detects files with duplicate contents. This paper describes the design and implementation of SIS in detail, briefly presents measurements of a remote install server showing a 58 % disk space savings by using SIS, and discusses other possible uses of SIS. 1.

To enable computer designers to better evaluate the architectural needs of operating systems, we have developed

Recently, lightweight thread libraries have become a common entity to support concurrent programming on shared memory multiprocessors. However, the disparity between primitives offered by operating systems creates a challenge for those who wish to create portable lightweight thread packages. What should be the interface between the machine-independent and machine-dependent parts of the thread library ? We have implemented a portable lightweight thread library on top of Unix on a KSR-1 supercomputer, BBN Butterfly multiprocessor, SGI multiprocessor, Sequent multiprocessor and Sun 3/4 family of uniprocessors. This paper first compares the nature and performance of the OS primitives offered by these machines. We then present a procedure-level abstraction that is efficiently implementable on all the architectures and is a sufficient base upon which a user-level thread package can be built. College of Computing Georgia Institute of Technology Atlanta, Georgia 30332--0280 1 Introduction T...