4 Commits

Author	SHA1	Message	Date
Martin Whitaker	f6da06b117	Work around the halt/wakeup race in barrier_halt_wait() (issue #13) ... There is an unavoidable race between one core halting after decrementing the barrier count and another core sending it the wakeup NMI. This can only occur if the core sending the wakeup is running at many times the speed of the core halting, but it has been observed on an Intel Icelake mobile processor.	2022-03-08 23:25:16 +00:00
Martin Whitaker	0076e63885	Optimise the barrier wait code. ... This reduces the number of instructions between decrementing the count and halting in the halt wait case. Use the same code for the spin wait case for consistency.	2022-03-08 23:25:16 +00:00
Martin Whitaker	4078b7760e	Faster barrier implementation. ... The old barrier implementation was very slow when running on a multi-socket machine (pcmemtest issue 16). The new implementation provides two options: - when blocked, spin on a thread-local flag - when blocked, execute a HLT instruction and wait for a NMI The first option might be faster, but we need to measure it to find out. A new boot command line option is provided to select between the two, with a third setting that uses a mixture of the two.	2022-02-28 22:05:21 +00:00
Martin Whitaker	fbd3376668	Initial commit.	2020-05-24 21:30:55 +01:00