Sort of agree, although my intuition tells me not that there's an excessively-coarse-locking problem, but that there's most likely a contention problem. The es

Sort of agree, although my intuition tells me not that there's an excessively-coarse-locking problem, but that there's most likely a contention problem. The essence of a contention problem, for those who don't know, is that some shared structure (maybe a counter, or the head of a queue, or something) is polled and updated for every message that needs to be processed. Since processors don't (usually) share their caches, updating a value in shared memory causes that cache line on the other processors to be invalidated, so the next time the other processor needs to poll that value it has to retrieve it from memory, which takes a lot of extra time compared to getting it off the L1. This problem often arises with shared work queues and counters. For work queues you can solve it by giving each processor its own work queue and having it steal work from other processors when it finishes its own queue. A textbook by Herlihy and Shavit, The Art of Multiprocessor Programming, discusses this stuff in detail.