On Fri, Aug 05, 2005 at 19:35:14 +0100, Tristan Wibberley wrote: > I wrote: > > > There is also Ingo Molnar's (and probably others') RT-PREEMPT patches > > currenty under development. These really do try to get nearly every > > point preemtible. Drivers should synchronise with semaphores, mutexes > > (which both do priority inheritance), and completions. > > I think that's a bit wrong. It doesn't make sense for a semaphore to do > priority inheritance as the whole point of a semaphore is that things > are supposed to receive notification when something has finished, and > the thing that does the notifying does not try to make progress for the > waiters. While a mutex identifies a critical section and the > process/thread holding the mutex moves out of the way quickly when a > high priority thread/process is waiting (essentially starts making rapid > progress for the benefit of the waiter, since the waiter has important > things to do). In kernel there is NO PRIMITIVE CALLED MUTEX. It is a special case of semaphore. Thus it is the semaphore that has to do priority inheritance. There are also spin-locks, which are conceptually mutexes, but they are special in that they disable preemption -- the real-time patches need to reduce the span of these. Notifications when something is finished are usually sent using wait-queues (which are "conditional variables") and completions (which are rather similar to semaphores). ------------------------------------------------------------------------------- Jan 'Bulb' Hudec <bulb@xxxxxx>
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