threads/118910: Multithreading problem

[Daniel Eischen]

On Fri, 21 Dec 2007, David Xu wrote:

> Daniel Eischen wrote:
>
>> I don't think it is as big a change as you think it is.  We already
>> have several layers of priorities (interrupt, time-share, idle, ?).
>> All threads belong to these classes.  As long as priority inheritence
>> works, there should be no problems.  The problems seem to occur when
>> we try to inject artificial priorities into threads, like using
>> msleep().  I think we are better off just letting threads run based
>> on their own base priority and whatever their inherited priority is.
>> 
>
> For test purpose, you may try to ignore thread priority parameter
> in msleep(), I didn't test this, but it does change the FreeBSD
> behavior. I don't know any side effect since I am unable to test
> all applications in the world, maybe you can start a project to hack
> it ?

I'll take a look at trying that.  I should be able to figure out
how to get msleep to ignore the priority.  But I think the missing
piece is the interrupt routines - they need to create their mutexes
and CVs so that they are more like priority ceiling mutexes.  Any
thread (even non-interrupt threads) that takes one of these mutexes
needs to have its priority raised as well as blocking the interrupt
(for fast interrupts anyway) until the mutex is released.

-- 
DE