The best case numbers for the interrupt-transparent implementation
of both enqueue() and dequeue() indicate
the overhead of these two primitives for the assumed
normal situation in which no interruption takes place. This
situation is considered normal not only because a single interrupt
at a time is a fairly exceptional event, but also because
overlapping interrupts are much more exceptional.
The critical and somewhat overhead-prone case comes up
only when enqueue() (1) gets interrupted at sensitive locations
and (2) could be thus overlapped by itself and when
(3) the interrupting instance shares the same queue with the
interrupted instances. Even for stressed systems this combination
of events is of quite low probability.