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509
Logtm: Log-based transactional memory
- in HPCA
, 2006
"... Transactional memory (TM) simplifies parallel programming by guaranteeing that transactions appear to execute atomically and in isolation. Implementing these properties includes providing data version management for the simultaneous storage of both new (visible if the transaction commits) and old (r ..."
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Cited by 282 (11 self)
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Transactional memory (TM) simplifies parallel programming by guaranteeing that transactions appear to execute atomically and in isolation. Implementing these properties includes providing data version management for the simultaneous storage of both new (visible if the transaction commits) and old (retained if the transaction aborts) values. Most (hardware) TM systems leave old values “in place” (the target memory address) and buffer new values elsewhere until commit. This makes aborts fast, but penalizes (the much more frequent) commits. In this paper, we present a new implementation of transactional memory, Log-based Transactional Memory (LogTM), that makes commits fast by storing old values to a per-thread log in cacheable virtual memory and storing new values in place. LogTM makes two additional contributions. First, LogTM extends a MOESI directory protocol to enable both fast conflict detection on evicted blocks and fast commit (using lazy cleanup). Second, LogTM handles aborts in (library) software with little performance penalty. Evaluations running micro- and SPLASH-2 benchmarks on a 32way multiprocessor support our decision to optimize for commit by showing that only 1-2 % of transactions abort. 1.
On the correctness of transactional memory.
- In PPoPP.
, 2008
"... Abstract. We introduce the notion of permissiveness in transactional memories (TM). Intuitively, a TM is permissive if it never aborts a transaction when it need not. More specifically, a TM is permissive with respect to a safety property p if the TM accepts every history that satisfies p. Permissi ..."
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Cited by 212 (27 self)
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Abstract. We introduce the notion of permissiveness in transactional memories (TM). Intuitively, a TM is permissive if it never aborts a transaction when it need not. More specifically, a TM is permissive with respect to a safety property p if the TM accepts every history that satisfies p. Permissiveness, like safety and liveness, can be used as a metric to compare TMs. We illustrate that it is impractical to achieve permissiveness deterministically, and then show how randomization can be used to achieve permissiveness efficiently. We introduce Adaptive Validation STM (AVSTM), which is probabilistically permissive with respect to opacity; that is, every opaque history is accepted by AVSTM with positive probability. Moreover, AVSTM guarantees lock freedom. Owing to its permissiveness, AVSTM outperforms other STMs by upto 40% in read dominated workloads in high contention scenarios. But, in low contention scenarios, the bookkeeping done by AVSTM to achieve permissiveness makes it, on average, 20-30% worse than existing STMs.
Parallel Programmability and the Chapel Language
- Int. J. High Perform. Comput. Appl
"... It is an increasingly common belief that the programmability of parallel machines is lacking, and that the high-end computing (HEC) community is suffering as a result of it. The population of users who can effectively program parallel machines comprises only a small fraction of those who can effecti ..."
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Cited by 193 (8 self)
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It is an increasingly common belief that the programmability of parallel machines is lacking, and that the high-end computing (HEC) community is suffering as a result of it. The population of users who can effectively program parallel machines comprises only a small fraction of those who can effectively program traditional sequential computers, and this gap seems only to be widening as time passes. The parallel computing community’s inability to tap the skills
Hybrid transactional memory
- IN PROC. 12TH INTERNATIONAL CONFERENCE ON ARCHITECTURAL SUPPORT FOR PROGRAMMING LANGUAGES AND OPERATING SYSTEMS (ASPLOSXII
, 2006
"... Transactional memory (TM) promises to substantially reduce the difficulty of writing correct, efficient, and scalable concurrent programs. But “bounded ” and “best-effort” hardware TM proposals impose unreasonable constraints on programmers, while more flexible software TM implementations are consid ..."
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Cited by 173 (11 self)
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Transactional memory (TM) promises to substantially reduce the difficulty of writing correct, efficient, and scalable concurrent programs. But “bounded ” and “best-effort” hardware TM proposals impose unreasonable constraints on programmers, while more flexible software TM implementations are considered too slow. Proposals for supporting “unbounded” transactions in hardware entail significantly higher complexity and risk than best-effort designs. We introduce Hybrid Transactional Memory (HyTM), an approach to implementing TM in software so that it can use best-effort hardware TM (HTM) to boost performance but does not depend on HTM. Thus programmers can develop and test transactional programs in existing systems today, and can enjoy the performance benefits of HTM support when it becomes available. We describe our prototype HyTM system, comprising a compiler and a library. The compiler allows a transaction to be attempted using best-effort HTM, and retried using the software library if it fails. We have used our prototype to “transactify ” part of the Berkeley DB system, as well as several benchmarks. By disabling the optional use of HTM, we can run all of these tests on existing systems. Furthermore, by using a simulated multiprocessor with HTM support, we demonstrate the viability of the HyTM approach: it can provide performance and scalability approaching that of an unbounded HTM implementation, without the need to support all transactions with complicated HTM support.
Compiler and Runtime Support for Efficient Software Transactional Memory
, 2006
"... Programmers have traditionally used locks to synchronize concurrent access to shared data. Lock-based synchronization, however, has well-known pitfalls: using locks for fine-grain synchronization and composing code that already uses locks are both difficult and prone to deadlock. Transactional memor ..."
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Cited by 159 (10 self)
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Programmers have traditionally used locks to synchronize concurrent access to shared data. Lock-based synchronization, however, has well-known pitfalls: using locks for fine-grain synchronization and composing code that already uses locks are both difficult and prone to deadlock. Transactional memory provides an alternate concurrency control mechanism that avoids these pitfalls and significantly eases concurrent programming. Transactional memory language constructs have recently been proposed as extensions to existing languages or included in new concurrent language specifications, opening the door for new compiler optimizations that target the overheads of transactional memory. This paper presents compiler and runtime optimizations for transactional memory language constructs. We present a highperformance software transactional memory system (STM) integrated into a managed runtime environment. Our system efficiently implements nested transactions that support both composition of transactions and partial roll back. Our JIT compiler is the first to optimize the overheads of STM, and we show novel techniques for enabling JIT optimizations on STM operations. We measure the performance of our optimizations on a 16-way SMP running multi-threaded transactional workloads. Our results show that these techniques enable transactional memory’s performance to compete with that of well-tuned synchronization.
Dynamic Performance Tuning of Word-Based Software Transactional Memory
"... The current generation of software transactional memories has the advantage of being simple and efficient. Nevertheless, there are several parameters that affect the performance of a transactional memory, for example the locality of the application and the cache line size of the processor. In this p ..."
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Cited by 140 (15 self)
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The current generation of software transactional memories has the advantage of being simple and efficient. Nevertheless, there are several parameters that affect the performance of a transactional memory, for example the locality of the application and the cache line size of the processor. In this paper, we investigate dynamic tuning mechanisms on a new time-based software transactional memory implementation. We study in extensive measurements the performance of our implementation and exhibit the benefits of dynamic tuning. We compare our results with TL2, which is currently one of the fastest word-based software transactional memories. D.1.3 [Programming Tech-
A flexible framework for implementing software transactional memory
- In ACM Conference on Object-Oriented Programming, Systems, Languages, and Applications
, 2006
"... We describe DSTM2, a Java TM software library that provides a flexible framework for implementing object-based software transactional memory (STM). The library uses transactional factories to transform sequential (unsynchronized) classes into atomic (transactionally synchronized) ones, providing a s ..."
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Cited by 132 (5 self)
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We describe DSTM2, a Java TM software library that provides a flexible framework for implementing object-based software transactional memory (STM). The library uses transactional factories to transform sequential (unsynchronized) classes into atomic (transactionally synchronized) ones, providing a substantial improvement over the awkward programming interface of our previous DSTM library. Furthermore, researchers can experiment with alternative STM mechanisms by providing their own factories. We demonstrate this flexibility by presenting two factories: one that uses essentially the same mechanisms as the original DSTM (with some enhancements), and another that uses a completely different approach. Because DSTM2 is packaged as a Java library, a wide range of programmers can easily try it out, and the community can begin to gain experience with transactional programming. Furthermore, researchers will be able to use the body of transactional programs that arises from this community experience to test and evaluate different STM mechanisms simply by supplying new transactional factories. We believe that this flexible approach will help to build consensus about the best ways to implement transactions, and will avoid the premature “lock-in ” that may arise if STM mechanisms are baked into compilers before such experimentation is done.
Concurrent Programming Without Locks
, 2004
"... Mutual exclusion locks remain the de facto mechanism for concurrency control on shared-memory data structures. However, their apparent simplicity is deceptive: it is hard to design scalable locking strategies because locks can harbour problems such as priority inversion, deadlock and convoying. Furt ..."
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Cited by 124 (4 self)
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Mutual exclusion locks remain the de facto mechanism for concurrency control on shared-memory data structures. However, their apparent simplicity is deceptive: it is hard to design scalable locking strategies because locks can harbour problems such as priority inversion, deadlock and convoying. Furthermore, scalable lock-based systems are not readily composable when building compound operations. In looking for solutions to these problems, interest has developed in nonblocking systems which have promised scalability and robustness by eschewing mutual exclusion while still ensuring safety. However, existing techniques for building non-blocking systems are rarely suitable for practical use, imposing substantial storage overheads, serialising non-conflicting operations, or requiring instructions not readily available on today’s CPUs. In this paper we present three APIs which make it easier to develop non-blocking implementations of arbitrary data structures. The first API is a multi-word compare-and-swap operation (MCAS) which atomically updates a set of memory locations. This can be used to advance a data structure from one consistent state to another. The second API is a word-based software transactional memory (WSTM) which can allow sequential code to be re-used more directly than with MCAS and which provides better scalability when locations are being read rather than being
Associating synchronization constraints with data in an object-oriented language
- In Proceedings of the ACM Symposium on the Principles of Programming Languages
, 2006
"... Concurrency-related bugs may happen when multiple threads access shared data and interleave in ways that do not correspond to any sequential execution. Their absence is not guaranteed by the traditional notion of “data race ” freedom. We present a new definition of data races in terms of 11 problema ..."
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Cited by 123 (6 self)
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Concurrency-related bugs may happen when multiple threads access shared data and interleave in ways that do not correspond to any sequential execution. Their absence is not guaranteed by the traditional notion of “data race ” freedom. We present a new definition of data races in terms of 11 problematic interleaving scenarios, and prove that it is complete by showing that any execution not exhibiting these scenarios is serializable for a chosen set of locations. Our definition subsumes the traditional definition of a data race as well as high-level data races such as stale-value errors and inconsistent views. We also propose a language feature called atomic sets of locations, which lets programmers specify the existence of consistency properties between fields in objects, without specifying the properties themselves. We use static analysis to automatically infer those points in the code where synchronization is needed to avoid data races under our new definition. An important benefit of this approach is that, in general, far fewer annotations are required than is the case with existing approaches such as synchronized blocks or atomic sections. Our implementation successfully inferred the appropriate synchronization for a significant subset of Java’s Standard Collections framework.
