SCHED_DEADLINE (new version of SCHED_EDF)

Hi Peter, Hi all,

Given all the comments and feedback we got, here it is the new version
of our EDF patch, this time in a split series. :-)

Special thanks to all the one that gave us any kind of suggestion,
especially during last RTLWS in Dresden.

The rationale/motivation for the new scheduler is the same of the first
e-mail (http://lwn.net/Articles/353797/), thus I only add some new and
(I think) interesting links:
 - Ericsson posting about SCHED_EDF/DEADLINE
    https://labs.ericsson.com/blog/making-linux-more-real-time

 - The slides we presented at RTLWS in Dresden:
    http://retis.sssup.it/people/faggioli/sched_deadline/rtlw...

 - Luca Abeni's presentation about using deadline based reservation 
   schedulers for IRQ-Threads:
    http://www.disi.unitn.it/~abeni/rtlws-slides.pdf

Moreover, we moved the project on gitorious.org, therefore:
 http://gitorious.org/sched_deadline

I am also setting up right now the Wiki section, where you can find some
more detailed usage instructions, examples and overhead estimation:
 http://gitorious.org/sched_deadline/pages/Home

Git repositories are up and running, and ready at:
(mainline)
 git://gitorious.org/sched_deadline/linux-deadline.git sched-deadline 

(sched-devel)
 git://gitorious.org/sched_deadline/linux-deadline.git sched-devel-deadline

(preempt-rt [*])
 git://gitorious.org/sched_deadline/linux-deadline.git rt-deadline

The new project homepage is
 http://www.evidence.eu.com/sched_deadline.html

Here the main changes we did, following what many of you --and mainly
Peter-- suggested:
- name changed from SCHED_EDF to SCHED_DEADLINE

- SCHED_DEADLINE has higher priority than SCHED_FIFO/SCHED_RR

- flags added in sched_param_ex to signal deadline misses
  (in case of utilization > 100%) and/or budget overruns

- new sched_*_ex prototypes, with a len field to accomodate the size of
  sched_param_ex, trying to avoid further ABI issues if it changes

- new syscall sched_wait_interval added. It behaves like clock_nanosleep
  but, for a SCHED_DEADLINE task, it also represent the end of the
  current instance (sched_yield no longer needed)

- on fork, child starts but with 0 bandwidth (i.e., it does not start! :-D)

- bug fixing :)

Any feedback and contribution is welcome.

Many thanks,

             Dario Faggioli
             Claudio Scordino
             Michael Trimarchi

[*] porting toward preempt-rt is work in progress. Code is there, but we
are testing and fixing it, with the help of Luca and Nicola from
Trento... So don't consider it as the final version!