When is to preempt safe?

[michi1 at michaelblizek.twilightparadox.com]

Hi!

On 19:52 Sun 09 Oct     , Parmenides wrote:
> 2011/10/9 Daniel Baluta <daniel.baluta at gmail.com>:
> > On Sat, Oct 8, 2011 at 7:19 PM, Parmenides <mobile.parmenides at gmail.com> wrote:
> >
> > Well, I think that if task B has higher priority than task A, then A would
> > never have the chance to release the lock.
> >
> 
> Hmm...!  Does that mean lower priority tasks never have chances to run
> when a highest priority task is running? AFAIK, for the old O(1)
> scheduler, even with higher priority, B eventually will be put into
> expire array when it using up its timeslice. That cause A has chance
> to run again. As far as the newer CFS scheduler is concerned,  when
> B's virtual clock is go ahead prior to A, the the scheduler might also
> select A to run again. So, I think A can release the spin lock
> eventually.

This is true for "normal" priorities. For real time tasks this is different:
The kernel always runs the task with the highest priority. However, a few
years ago, a throttle mechanism was implemented because real time tasks
occasionally locked up the system.

	-Michi
-- 
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.twilightparadox.com