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Transactional memory has been receiving much attention from both academia and industry. In transactional memory, program code is split into transactions, blocks of code that appear to execute atomically. Transactions are executed speculatively and the speculative execution is supported through data versioning mechanism. Lazy versioning makes aborts fast but penalizes commits, whereas eager versioning makes commits fast but penalizes aborts. However, whether to use eager or lazy versioning to execute those transactions is still a hotly debated topic. Lazy versioning seems appropriate for write-dominated workloads and transactions in high contention scenarios whereas eager versioning seems appropriate for read-dominated workloads and transactions in low contention scenarios. This necessitates a priori knowledge on the workload and contention scenario to select an appropriate versioning method to achieve better performance. In this article, we present an adaptive versioning approach, called Adaptive, that dynamically switches between eager and lazy versioning at runtime, without the need of a priori knowledge on the workload and contention scenario but based on appropriate system parameters, so that the performance of a transactional memory system is always better than that is obtained using either eager or lazy versioning individually. We provide Adaptive for both persistent and non-persistent transactional memory systems using performance parameters appropriate for those systems. We implemented our adaptive versioning approach in the latest software transactional memory distribution TinySTM and extensively evaluated it through 5 micro-benchmarks and 8 complex benchmarks from STAMP and STAMPEDE suites. The results show significant benefits of our approach. Specifically, in persistent TM systems, our approach achieved performance improvements as much as 1.5× for execution time and as much as 240× for number of aborts, whereas our approach achieved performance improvements as much as 6.3× for execution time and as much as 170× for number of aborts in non-persistent transactional memory systems.
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Leveraging hardware TM in Haskell
Transactional memory (TM) is heavily used for synchronization in the Haskell programming language, but its performance has historically been poor. We set out to improve this performance using hardware TM (HTM) on Intel processors. This task is complicated by Haskell's retry mechanism, which requires information to escape aborted transactions, and by the heavy use of indirection in the Haskell runtime, which means that even small transactions are likely to over-flow hardware buffers. It is eased by functional semantics, which preclude irreversible operations; by the static separation of transactional state, which precludes privatization; and by the error containment of strong typing, which enables so-called lazy subscription to the lock that protects the "fallback" code path. We describe a three-level hybrid TM system for the Glasgow Haskell Compiler (GHC). Our system first attempts to perform an entire transaction in hardware. Failing that, it falls back to software tracking of read and write sets combined with a commit-time hardware transaction. If necessary, it employs a global lock to serialize commits (but still not the bodies of transactions). To get good performance from hardware TM while preserving Haskell semantics, we use Bloom filters for read and write set tracking. We also implemented and extended the newly proposed mutable constructor fields language feature to significantly reduce indirection. Experimental results with complex data structures show significant improvements in throughput and scalability.
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- PAR ID:
- 10113198
- Date Published:
- Journal Name:
- Proceedings of the 24th Symposium on Principles and Practice of Parallel Programming
- Page Range / eLocation ID:
- 94 to 106
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3293883.3295711
