"Spinlocks are the lowest-level mutual exclusion mechanism in
the Linux kernel. As such, they have a great deal of influence over
the safety and performance of the kernel, so it is not surprising
that a great deal of optimization effort has gone into the various
(architecture-specific) spinlock implementations. That does not
mean that all of the work has been done, though; a patch merged for
2.6.25 shows that there is always more which can be done.
"On the x86 architecture, in the 2.6.24 kernel, a spinlock is
represented by an integer value..."