D. SUMMARY

At this point, it does not appear that any one approach can be all things to all realtime applications. It is therefore too early to pick a winner. Advocates of a given approach are therefore advised to concentrate their energy on implementations of their favorite approach, rather than engaging in flamewars with advocates of other… approaches. ;-)

After all, in the end, the approaches that best meet the needs of the user community will win out. In fact, given that the Linux community has come up with no fewer than seven classes of solutions to a problem that is commonly thought to be unsolvable, it seems quite reasonable to expect that yet more classes of solutions will yet appear.

So, which of these approaches can be combined? The first three can be thought of as elaborations on the general preemption theme, and can be combined with each of the remaining four. The nested-OS and dual-OS/dual-core ideas can be combined by having one of the OSes on one of the cores have another OS nested within it. The dual-core/dual-OS approach can be combined with either of the migration approaches, simply by having one of the cores implement the migration approach. It should be possible to combine the two migration approaches, though it is not clear that this is useful.

Regardless of whether Linux's direction ends up being a single one of these approaches, a yet-as-unknown approach, or some combination, realtime Linux looks to remain an exciting area.

About the author — Paul E. McKenney is a distinguished engineer at IBM and has worked on SMP, NUMA, and RCU algorithms for longer than he cares to admit. Prior to that, he worked on packet-radio and Internet protocols (but long before the Internet became popular), system administration, realtime systems, and even business applications. His hobbies include running and the usual house-wife-and-kids habit.