> > > > 2. Isn't it possible to get in trouble even on a UP if a task
> > > > is preempted in a critical region? For example, suppose the
> > > > preempting task does a synchronize_kernel()?
> > >
> > > Ugly. I guess one way to solve it would be to readd the 2.2 scheduler
> > > taskqueue, and just queue a scheduler callback in this case.
> >
> > Another approach would be to define a "really low" priority that noone
> > other than synchronize_kernel() was allowed to use. Then the UP
> > implementation of synchronize_kernel() could drop its priority to
> > this level, yield the CPU, and know that all preempted tasks must
> > have obtained and voluntarily yielded the CPU before synchronize_kernel
()
> > gets it back again.
>
> That just would allow nasty starvation, e.g. when someone runs a cpu
intensive
> screensaver or a seti-at-home.
Good point! I hereby withdraw my suggested use of ultra-low priorities
for UP implementations of synchronize_kernel(). ;-)
> > I still prefer suppressing preemption on the read side, though I
> > suppose one could claim that this is only because I am -really-
> > used to it. ;-)
>
> For a lot of reader cases non-preemption by threads is guaranteed anyways
--
> e.g. anything that runs in interrupts, timers, tasklets and network
softirq.
> I think that already covers a lot of interesting cases.
Good point again! For example, this does cover most of the TCP/IP
cases, right?
Thanx, Paul
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