[RFC] Some new generic device features.

[Robert Watson]

On Fri, 1 Feb 2008, Maxim Zhuravlev wrote:

> 2008/1/31, Hans Petter Selasky <hselasky at c2i.net>:
>
>> Some general comments:
>>
>> How does it handle mutexes?
>
> By now mutexes are used by io subsystem: All input/output requests (iors) 
> and queues of iors are guarded by spin mutexes. As for devices, their NewBus 
> sided structures will be guarded by (spin?) mutexes.

Generic question: is it desirable/necessary to do this using [solely] spin 
mutexes?  They are more expensive than regular mutexes (since they also 
disable interrupts), and are not generally necessary unless code is running 
under the scheduler or in a fast interrupt context.  There are good reasons to 
write device driver code that runs in the fast interrupt context, but serious 
work (i.e., passing things up and down higher level stacks such as CAM, the 
network stack, ttys, etc) generally happens outside of that context.  If some 
of this necessarily runs in those sensitive contexts, is it the case that it 
mostly does?

Robert N M Watson
Computer Laboratory
University of Cambridge