Existing best-effort requester-wins implementations of transactional memory must resort to non-speculative execution to provide forward progress in the presence of transactions that exceed hardware capacity, experience page faults or suffer high-contention leading to livelocks. Current approaches to irrevocability employ lock-based synchronization to achieve mutual exclusion when executing a transaction non-speculatively, conservatively precluding concurrency with any other transactions in order to guarantee atomicity at the cost of degrading performance. In this article, we propose a new form of concurrent irrevocability whose goal is to minimize the loss of concurrency paid when transactions resort to irrevocability to complete. By enabling optimistic concurrency control also during non-speculative execution of a transaction, our proposal allows for higher parallelism than existing schemes. We describe the extensions to the instruction set to provide concurrent irrevocable transactions as well as the architectural extensions required to realize them on a best-effort HTM system without requiring any modification to the cache coherence protocol. Our evaluation shows that our proposal achieves an average reduction of 12.5 percent in execution time across the STAMP benchmarks, with 15.8 percent on average for highly contended workloads.

中文翻译：

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尽力而为硬件事务内存中的并发不可撤销性

事务内存的现有尽力而为请求者获胜实现必须诉诸非推测执行，以在存在超过硬件容量、经历页面错误或遭受导致活锁的高争用的事务的情况下提供前进进展。当前的不可撤销性方法采用基于锁的同步来在非推测性地执行事务时实现互斥，保守地排除与任何其他事务的并发性，以降低性能为代价保证原子性。在本文中，我们提出了一种新形式的并发不可撤销性，其目标是将交易诉诸不可撤销性来完成时支付的并发性损失降至最低。通过在事务的非推测执行期间启用乐观并发控制，我们的提议允许比现有方案更高的并行性。我们描述了指令集的扩展，以提供并发不可撤销的事务，以及在尽力而为的 HTM 系统上实现它们所需的架构扩展，而不需要对缓存一致性协议进行任何修改。我们的评估表明，我们的提案在 STAMP 基准测试中平均减少了 12.5% 的执行时间，对于高度竞争的工作负载平均减少 15.8%。