Maximum benefit from a minimal HTM

  • Authors:

  • Owen S. Hofmann;Christopher J. Rossbach;Emmett Witchel

  • Affiliations:

  • University of Texas at Austin, Austin, TX, USA;University of Texas at Austin, Austin, TX, USA;University of Texas at Austin, Austin, TX, USA

  • Venue:
  • Proceedings of the 14th international conference on Architectural support for programming languages and operating systems
  • Year:
  • 2009

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Abstract

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% of the performance gap with the Linux 2.6 kernel, which has 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 minimal coupling between hardware and software systems. There is no performance penalty for overflow rates of less than 1%. In one instance, at 16 processors and an overflow rate of 4%, performance degrades from an ideal 4.3x to 3.6x.