> So what exactly _is_ the difference between an explicit
> preemption point and a place where we need to explicitly
> drop a spinlock ?
In that case nothing, except that when we drop the lock and check it is
the earliest place where preemption is allowed. In the normal scenario,
however, we have a check for reschedule on return from interrupt (e.g.
the timer) and thus preempt in the same manner as with user space and
that is the key.
> > Future work would be to look into long-held locks and see what we can
> > do.
> One thing we could do is download Andrew Morton's patch ;)
That is certainly one option, and Andrew's patch is very good.
Nonetheless, I think we need a more general framework that tackles the
problem itself. Preemptible kernel does this, yields results now, and
allows for greater return later on.
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