I think the important practical distinction is whether or not these stalls imply a context switch. Software that avoids blocking calls is largely trying to mini

I think the important practical distinction is whether or not these stalls imply a context switch. Software that avoids blocking calls is largely trying to minimize context switches, with measurable adverse effects being increasingly common due to improvements in hardware. Stalls that do not imply context switches, such as filling a cache line, are not "blocking" as a matter of practical semantics because there is no context switch that has to be accounted for. Of course, this gets into a gray area with things like hyper-threading that have some of the side-effects of a context switch without an actual context switch.