How Linux prioritizes activities

Now that you have learned about so many areas across the gamut, we can zoom out and see how the Linux kernel prioritizes things. The following (conceptual) diagram - a superset of earlier similar diagrams - neatly sums this up:

Figure 4.13 – Relative priorities across the full stack - user, kernel process context, and kernel interrupt contexts

This diagram is pretty self-explanatory, so please study it carefully.

In this lengthy section, you have learned about interrupt handling via both the top-half and bottom-half mechanisms, the reasons for them in the first place, and how they are organized and to be used by drivers. You now understand that all bottom-half mechanisms are internally implemented via softirqs; the tasklet is the primary bottom-half mechanism that you, as a driver author, have easy access to use. This, of course, does not imply you must use them – if you can get away with simply using a top-half only, or, even...