TxLinux is a variant of Linux that is the first operating system to use hardware transactional memory (HTM) as a synchronization primitive, and the first to manage HTM in the scheduler. This paper describes and measures TxLinux and discusses two innovations in detail: cooperation between locks and transactions, and the integration of transactions with the OS scheduler. Mixing locks and transactions requires a new primitive, cooperative transactional spinlocks (cxspinlocks) that allow locks and transactions to protect the same data while maintaining the advantages of both synchronization primitives. Cxspinlocks allow the system to attempt execution of critical regions with transactions and automatically roll back to use locking if the region performs I/O. Integrating the scheduler with HTM eliminates priority inversion. On a series of real-world benchmarks TxLinux has similar performance to Linux, exposing concurrency with as many as 32 concurrent threads on 32 CPUs in the same critical region.

TxLinux is the first operating system to use hardware transactional memory (HTM) as a synchronization primitive, and the first to manage HTM in the scheduler. TxLinux, which is a modification of Linux, is the first real-scale benchmark for transactional memory. MetaTM is a modification of the x86 architecture that supports HTM in general and TxLinux specifically. This paper describes and measures TxLinux and MetaTM, the hardware transactional memory model that supports it. TxLinux greatly benefits from a new primitive, called the cooperative transactional spinlock (cxspinlock) that allows locks and transactions to protect the same data while maintaining the advantages of both synchronization primitives. Integrating the TxLinux scheduler with the MetaTM’s architectural support for HTM eliminates priority inversion for several real-world benchmarks. 1.

A minimal, bounded hardware transactional memory implementation significantly improves synchronization performance when used in an operating system kernel. We add HTM to Linux 2.4, a kernel with a simple, coarse-grained synchronization structure. The transactional Linux 2.4 kernel can improve performance of user programs by as much as 40 % over the non-transactional 2.4 kernel. It closes 68% oftheperformancegapwiththeLinux2.6kernel,whichhas had significant engineering effort applied to improve scalability. We then extend our minimal HTM to a fast, unbounded transactional memory with a novel technique for coordinating hardware transactions and software synchronization. Overflowed transactions run in software, with only a minimalcouplingbetweenhardwareandsoftwaresystems.There isnoperformancepenaltyforoverflowratesoflessthan1%. Inoneinstance,at16processorsandanoverflowrateof4%, performance degrades from an ideal 4.3 × to3.6×.

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