On Tue, Jul 13, 2004 at 11:44:59PM +0100, Martijn Sipkema wrote: [...] There are cases where you have to use priority inheritance, but the schemes that are typically used either have a kind of exhaustive analysis backing it or uses a simple late detection scheme. In a general purpose OS, the latter is useful for various kind of overload cases. But if your system is constantly using that specific case, then it's a sign the contention in the kernel must *also* be a problem under SMP conditions. The constant use of priority inheritance overloads the scheduler, puts pressure on the cache and other negative things that hurt CPU local performance of the system. The reason why I mention this is because of Linux's hand-crafted nature of dealing with this. These are basically contention problems expressed in a different manner. The traditional Linux method is the correct method of deal with this in a general purpose OS. This also applies to application structure as well. The use of these mechanisms need to be thought out before application.

The nature these kind of applications push into a very demanding space where typical methodologies surrounding the use of threads goes out the window. Pushing both the IO and CPU resources of a kernel is the common case and often you have to roll your own APIs, synchronization mechanisms to deal with these problem. Simple Posix API and traditional mutexes are a bit too narrow in scope to solve these cross system concurrency problems. It's not trivial stuff at all and can span from loosely to tightly coupled systems, yes, all for pro-audio/video. Posix and friends in these cases simply aren't good enough to cut it.