Showing papers by "Michael Spear published in 2006"

Lowering the Overhead of Nonblocking Software Transactional Memory

Abstract: Recent years have seen the development of several dierent systems for software transactional memory (STM). Most either employ locks in the underlying implementation or depend on thread-safe general-purpose garbage collection to collect stale data and metadata. We consider the design of low-overhead, obstruction-free software transactional memory for non-garbage-collected languages. Our design eliminates dynamic allocation of transactional metadata and co-locates data that are separate in other systems, thereby reducing the expected number of cache misses on the common-case code path, while preserving nonblocking progress and requiring no atomic instructions other than single-word load, store, and compare-and-swap (or load-linked/store-conditional). We also employ a simple, epoch-based storage management system and introduce a novel conservative mechanism to make reader transactions visible to writers without inducing additional metadata copying or dynamic allocation. Experimental results show throughput significantly higher than that of existing nonblocking STM systems, and highlight significant, application-specific dierences among conflict detection and validation strategies.

Conflict detection and validation strategies for software tradsacfional memory

Abstract: In a software transactional memory (STM) system, conflict detection is the problem of determining when two transactions cannot both safely commit. Validation is the related problem of ensuring that a transaction never views inconsistent data, which might potentially cause a doomed transaction to exhibit irreversible, externally visible side effects. Existing mechanisms for conflict detection vary greatly in their degree of speculation and their relative treatment of read-write and write-write conflicts. Validation, for its part, appears to be a dominant factor-perhaps the dominant factor-in the cost of complex transactions. We present the most comprehensive study to date of conflict detection strategies, characterizing the tradeoffs among them and identifying the ones that perform the best for various types of workload. In the process we introduce a lightweight heuristic mechanism-the global commit counter-that can greatly reduce the cost of validation and of single-threaded execution. The heuristic also allows us to experiment with mixed invalidation, a more opportunistic interleaving of reading and writing transactions. Experimental results on a 16-processor SunFire machine running our RSTM system indicate that the choice of conflict detection strategy can have a dramatic impact on performance, and that the best choice is workload dependent. In workloads whose transactions rarely conflict, the commit counter does little to help (and can even hurt) performance. For less scalable applications, however-those in which STM performance has traditionally been most problematic-it can improve transaction throughput many fold.

Conflict detection and validation strategies for software transactional memory

Abstract: In a software transactional memory (STM) system, conflict detection is the problem of determining when two transactions cannot both safely commit. Validation is the related problem of ensuring that a transaction never views inconsistent data, which might potentially cause a doomed transaction to exhibit irreversible, externally visible side effects. Existing mechanisms for conflict detection vary greatly in their degree of speculation and their relative treatment of read-write and write-write conflicts. Validation, for its part, appears to be a dominant factor—perhaps the dominant factor—in the cost of complex transactions. We present the most comprehensive study to date of conflict detection strategies, characterizing the tradeoffs among them and identifying the ones that perform the best for various types of workload. In the process we introduce a lightweight heuristic mechanism—the global commit counter—that can greatly reduce the cost of validation and of single-threaded execution. The heuristic also allows us to experiment with mixed invalidation, a more opportunistic interleaving of reading and writing transactions. Experimental results on a 16-processor SunFire machine running our RSTM system indicate that the choice of conflict detection strategy can have a dramatic impact on performance, and that the best choice is workload dependent. In workloads whose transactions rarely conflict, the commit counter does little to help (and can even hurt) performance. For less scalable applications, however—those in which STM performance has traditionally been most problematic—it can improve transaction throughput many fold.

Solving the starting problem: device drivers as self-describing artifacts

Abstract: Run-time conflicts can affect even the most rigorously tested software systems. A reliance on execution-based testing makes it prohibitively costly to test every possible interaction among potentially thousands of programs with complex configurations. In order to reduce configuration problems, detect developer errors, and reduce developer effort, we have created a new first class operating system abstraction, the application abstraction, which enables both online and offline reasoning about programs and their configuration requirements.We have implemented a subset of the application abstraction for device drivers in the Singularity operating system. Programmers use the application abstraction by placing declarative statements about hardware and communication requirements within their code. Our design enables Singularity to learn the input/output and interprocess communication requirements of drivers without executing driver code. By reasoning about this information within the domain of Singularity's strong software isolation architecture, the installer can execute a subset the system's resource management algorithm at install time to verify that a new driver will not conflict with existing software. This abstract representation also allows the system to run the full algorithm at driver start time to ensure that there are never resource conflicts between executing drivers, and that drivers never use undeclared resources.

Configuration of isolated extensions and device drivers

Abstract: Described herein are one or more implementations for describing and/or addressing the configuration requirements of applications, extensions, device drivers (300), and other components of a software system.