Alternating Threads

Could you point me in a direction for discovering how threads are being alternated in the Linux kern开发者_运维百科el?

Although I do not possess in depth knowledge about the kernel, but AFAIK to the kernel threads (& processes) appear as tasks. The switching between tasks is known as context switch. Context switch is triggered by scheduler through schedule call which is present in kernel/sched.c ( http://lxr.linux.no/linux+v3.0.4/kernel/sched.c#L4247 ). In schedule function context_switch is called which switches memory map & register values for the new thread. I would suggest looking at schedule function.
P.S.: You can use http://lxr.linux.no for browsing kernel code online.
Hope this helps!