During the development of the concurrent queues, and more narrowly the unbounded variants, was there a consideration of adding a backoff strategy? In particular an arena-based approach modeled after the elimination stack .
For a long time I've been meaning to explore the idea of a combining arena as a backoff strategy for producers. I implemented this on top of a mpsc linked queue  and observe a 70% gain when contended. The combined addition is a sublist that is appended atomically as one operation instead of many individual ones, which is an optimizations that is usually only available to #addAll(c).
The benchmark  was taken on a MacBook Pro i7-4870HQ CPU @ 2.50GHz (4 core). Note that the 8 producer benchmark is unfair for CLQ by using #clear() so that the consumer thread kept up with the producers.