Priority Inheritance in Linux Kernel

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According to LWN.net


There are a number of approaches to priority inheritance. In effect, the kernel performs a very simple form of it by not allowing kernel code to be preempted while holding a spinlock. In some systems, each lock has a priority associated with it; whenever a process takes a lock, its priority is raised to the lock's priority. In others, a high-priority process will have its priority "inherited" by another process which holds a needed lock. Most priority inheritance schemes have shown a tendency to complicate and slow down the locking code, and they can be used to paper over poor application designs. So they are unpopular in many circles. Linus was reasonably clear about how he felt on the subject last December:
"Friends don't let friends use priority inheritance".
Just don't do it. If you really need it, your system is broken anyway.
Faced with this sort of opposition, many developers would quietly shelve their priority inheritance designs and go back to working on accounting code. The kernel development community, however, happens to have a member who has a track record of getting code merged in spite of this sort of objection: Ingo Molnar. History may well repeat itself, as Ingo (working with Thomas Gleixner) has posted a priority-inheriting futex implementation with a request that it be merged into the mainline. This approach, says Ingo, provides a useful functionality to user space (it is not meant to provide priority-inheriting kernel mutual exclusion primitives) while avoiding the pitfalls which have hit other implementations.

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