The search for the correct amount of split-lock misery

prctl() is for things which affect the operation of the process itself. This controls whether a program making use of split locks can negatively impact the performance of the entire *system*, which puts it in a category similar to real-time priorities. As such, a privileged sysctl knob is a reasonable solution. A cgroup option could also work, and would allow access to split locks to be more precisely targeted, but it would need to require some form of elevated privilege to enable it for a regular user account.