Re: preemtive or non-prempteve ?

[Tristan Wibberley <maihem@xxxxxxxxxx>]

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).

-- 
Tristan Wibberley

Opinions expressed are my own and do not necessarily coincide with those
of my employer, etc.


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