On a certain computer we estimate that, regardless of the OS it runs, thread scheduling costs about 50 s, a null procedure call 1 s, a context switch to the kernel 20 s and a domain transition 40 s. For each of Mach and SPIN, estimate the cost to a client of calling a dynamically loaded null procedure.
What will be an ideal response?
Mach, by default, runs dynamically loaded code in a separate address space. So invoking the code involves control transfer to a thread in a separate address space. This involves four (context switch + domain transitions) to and from the kernel as well as two schedulings (client to server thread and server thread to client thread) -- in addition to the null procedure itself.
Estimated cost: 4(20 + 40) + 2*50 + 1 = 341 s
In SPIN, the call involve two (context switch + domain transitions) and no thread scheduling.
Estimated cost: 2(20 + 40) + 1 = 121 s.
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