Owen S. Hofmann, Christopher J. Rossbach, and Emmett Witchel
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 4.3× to 3.6×.