On Wed, Jan 30, 2019 at 10:01:35PM -0500, Alex Kogan wrote: > Choose the next lock holder among spinning threads running on the same > socket with high probability rather than always. With small probability, > hand the lock to the first thread in the secondary queue or, if that > queue is empty, to the immediate successor of the current lock holder > in the main queue. Thus, assuming no failures while threads hold the > lock, every thread would be able to acquire the lock after a bounded > number of lock transitions, with high probability. > > Note that we could make the inter-socket transition deterministic, > by sticking a counter of intra-socket transitions in the head node > of the secondary queue. At the handoff time, we could increment > the counter and check if it is below a threshold. This adds another > field to queue nodes and nearly-certain local cache miss to read and > update this counter during the handoff. While still beating stock, > this variant adds certain overhead over the probabilistic variant. (also heavily suffers from the socket == node confusion) How would you suggest RT 'tunes' this? RT relies on FIFO fairness of the basic spinlock primitives; you just completely wrecked that.
