My presentation about the real-time, EDF-based, scheduling classes and solutions for the Linux kernel at the 2010 edition of the Linux Kernel Summit.

1. Real-Time Deadline Scheduling and More...
Dario Faggioli
ReTiS Lab, Scuola Superiore Sant’Anna - Pisa (Italy),
10th Annual Linux KERNEL SUMMIT, Cambridge, MA
1st, November 2010
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

2. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

3. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

4. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

5. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

6. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

7. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

8. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

9. What is Real-Time?
Real-Time is all about determinism and guarantees:
guarantee that your system is deterministic,
achieve determinism, so that you can provide guarantees.
Classic Real-Time theory says:
”Hey, we can do that, just give us the following:
knowledge of how many and what task there will be,
knowledge of their periodicity and computation times,
either tasks are independent ...
... or you must know what, for how long and how many
times they access shared resources,
use uniprocessors ...
... or must run a schedulability test taking minutes ... For a
pessimistic result”
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

10. Resource Reservations
Task are reserved Q (runtime or budget) time units every T time
units (period) (i.e., they have a ”CPU bandwidth” of Q ).
P
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

11. Resource Reservations
Task are reserved Q (runtime or budget) time units every T time
units (period) (i.e., they have a ”CPU bandwidth” of Q ).
P
Applications get guaranteed CPU time, and misbehaviors are
confined within each task’s ”bandwidth capsule”.
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

12. Resource Reservations
Task are reserved Q (runtime or budget) time units every T time
units (period) (i.e., they have a ”CPU bandwidth” of Q ).
P
Applications get guaranteed CPU time, and misbehaviors are
confined within each task’s ”bandwidth capsule”.
τA
τB
0 2 4 6 8 10 12 14
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

13. Resource Reservations
Task are reserved Q (runtime or budget) time units every T time
units (period) (i.e., they have a ”CPU bandwidth” of Q ).
P
Applications get guaranteed CPU time, and misbehaviors are
confined within each task’s ”bandwidth capsule”.
τA
τB
0 2 4 6 8 10 12 14
τA
τB
0 2 4 6 8 10 12 14
τA
τB
0 2 4 6 8 10 12 14
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

14. What Applications are Real-Time? (I)
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

15. What Applications Are Real-Time? (II)
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

16. Concerning Latency... (I)
250000
low RT priority high RT priority CBS (12.5, 40) CBS (25, 40)
200000
150000
100000
50000
0
100 200 300 400 500 600 700 800100 200 300 400 500 600 700 800100 200 300 400 500 600 700 800100 200 300 400 500 600 700 800
Two concurrently running video players
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

17. Concerning Latency... (II)
1400
1200
1000
800
600
400
200 (1) CFS/CFS (2) FIFO/FIFO (3) FIFO/FIFO (4) AQuoSA/AQuoSA (5) SHRUB/SHRUB
0
0 10000 20000 30000 40000 0 10000 20000 30000 40000 0 10000 20000 30000 40000 0 10000 20000 30000 40000 0 10000 20000 30000 40000
80000
70000
60000
50000
40000
30000
20000
10000
0
0 500 1000 1500
0 500 1000 1500
0 500 1000 1500
0 500 1000 1500
0 500 1000 1500
JACK with 10 periodic clients plus a (fake!) real-time task
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

18. Concerning Throughput... (I)
80
70
60
50
Throughput (MB/s)
40
30
20
10
0
0 0.0005 0.001 0.0015 0.002 0.0025 0.003
Reserved fraction of CPU time (Q/T)
Disk throughput (DMA enabled).
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

19. Concerning Throughput... (II)
1.4
Minimum
Average
Maximum
1.2
1
Throughput (MB/s)
0.8
0.6
0.4
0.2
0
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Reserved fraction of CPU time
Disk throughput (without DMA).
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

20. Concerning Latency and Throughput...
A video player plus interrupt load by netperf.
250000
Player Alone Player + netperf Player with RT priority
+ netperf
200000
150000
100000
50000
0
100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800
Network throughput: -, 88 Mbps, 58 Mbps.
250000
CBS (20, 40) CBS (25, 40) CBS (29, 40)
200000
150000
100000
50000
0
100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800 100 200 300 400 500 600 700 800
Network throughput: 88 Mbps, 76 Mbps, 59 Mbps.
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

21. Can Linux Do This... (I)
With POSIX-like fix priority scheduling?
Yes, by means of implementing the SCHED SPORADIC
policy (part of POSIX).
Have a patch for that! :-)
With deadline-based scheduling (more convenient, sometimes more
efficient)?
Yes, by means of SCHED DEADLINE 1 and/or
EDF-throttling.
Have a patch for that! :-)
1
Together with Evidence s.r.l. within http://www.actors-project.eu
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

22. Can Linux Do This... (I)
With POSIX-like fix priority scheduling?
Yes, by means of implementing the SCHED SPORADIC
policy (part of POSIX).
Have a patch for that! :-)
With deadline-based scheduling (more convenient, sometimes more
efficient)?
Yes, by means of SCHED DEADLINE 1 and/or
EDF-throttling.
Have a patch for that! :-)
1
Together with Evidence s.r.l. within http://www.actors-project.eu
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

23. Can Linux Do This... (I)
With POSIX-like fix priority scheduling?
Yes, by means of implementing the SCHED SPORADIC
policy (part of POSIX).
Have a patch for that! :-)
With deadline-based scheduling (more convenient, sometimes more
efficient)?
Yes, by means of SCHED DEADLINE 1 and/or
EDF-throttling.
Have a patch for that! :-)
1
Together with Evidence s.r.l. within http://www.actors-project.eu
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

24. Can Linux Do This... (I)
With POSIX-like fix priority scheduling?
Yes, by means of implementing the SCHED SPORADIC
policy (part of POSIX).
Have a patch for that! :-)
With deadline-based scheduling (more convenient, sometimes more
efficient)?
Yes, by means of SCHED DEADLINE 1 and/or
EDF-throttling.
Have a patch for that! :-)
1
Together with Evidence s.r.l. within http://www.actors-project.eu
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

25. Can Linux Do This... (II)
I just released v3 of SCHED DEADLINE (last Friday).
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

26. Can Linux Do This... (II)
I just released v3 of SCHED DEADLINE (last Friday).
I planned to have more code ready by now, but I got preempted
by a very high priority ”task”, about a month ago...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

27. Can Linux Do This... (II)
I just released v3 of SCHED DEADLINE (last Friday).
I planned to have more code ready by now, but I got preempted
by a very high priority ”task”, about a month ago...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

28. Now, The Really Important Part...
... Questions and open issues:
Do you want this ?
In what fashion? Priorities? Deadlines? Hierarchical? All of
them ;-P) ?
With what user interface? New syscalls? Cgroupfs? Binary?
At what privilege level/with what security model? FIFO/RR
ones? Maybe less restrictions?
Are users/application-developers ever start using this (if it’s
accepted)? Is there something that can/needs to be done
toward this?
How to balance stability of the API(s) and the new feature
requests that might come out?
...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

29. Now, The Really Important Part...
... Questions and open issues:
Do you want this ?
In what fashion? Priorities? Deadlines? Hierarchical? All of
them ;-P) ?
With what user interface? New syscalls? Cgroupfs? Binary?
At what privilege level/with what security model? FIFO/RR
ones? Maybe less restrictions?
Are users/application-developers ever start using this (if it’s
accepted)? Is there something that can/needs to be done
toward this?
How to balance stability of the API(s) and the new feature
requests that might come out?
...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

30. Now, The Really Important Part...
... Questions and open issues:
Do you want this ?
In what fashion? Priorities? Deadlines? Hierarchical? All of
them ;-P) ?
With what user interface? New syscalls? Cgroupfs? Binary?
At what privilege level/with what security model? FIFO/RR
ones? Maybe less restrictions?
Are users/application-developers ever start using this (if it’s
accepted)? Is there something that can/needs to be done
toward this?
How to balance stability of the API(s) and the new feature
requests that might come out?
...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

31. Now, The Really Important Part...
... Questions and open issues:
Do you want this ?
In what fashion? Priorities? Deadlines? Hierarchical? All of
them ;-P) ?
With what user interface? New syscalls? Cgroupfs? Binary?
At what privilege level/with what security model? FIFO/RR
ones? Maybe less restrictions?
Are users/application-developers ever start using this (if it’s
accepted)? Is there something that can/needs to be done
toward this?
How to balance stability of the API(s) and the new feature
requests that might come out?
...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

32. Now, The Really Important Part...
... Questions and open issues:
Do you want this ?
In what fashion? Priorities? Deadlines? Hierarchical? All of
them ;-P) ?
With what user interface? New syscalls? Cgroupfs? Binary?
At what privilege level/with what security model? FIFO/RR
ones? Maybe less restrictions?
Are users/application-developers ever start using this (if it’s
accepted)? Is there something that can/needs to be done
toward this?
How to balance stability of the API(s) and the new feature
requests that might come out?
...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

33. Now, The Really Important Part...
... Questions and open issues:
Do you want this ?
In what fashion? Priorities? Deadlines? Hierarchical? All of
them ;-P) ?
With what user interface? New syscalls? Cgroupfs? Binary?
At what privilege level/with what security model? FIFO/RR
ones? Maybe less restrictions?
Are users/application-developers ever start using this (if it’s
accepted)? Is there something that can/needs to be done
toward this?
How to balance stability of the API(s) and the new feature
requests that might come out?
...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...

34. Now, The Really Important Part...
... Questions and open issues:
Do you want this ?
In what fashion? Priorities? Deadlines? Hierarchical? All of
them ;-P) ?
With what user interface? New syscalls? Cgroupfs? Binary?
At what privilege level/with what security model? FIFO/RR
ones? Maybe less restrictions?
Are users/application-developers ever start using this (if it’s
accepted)? Is there something that can/needs to be done
toward this?
How to balance stability of the API(s) and the new feature
requests that might come out?
...
D. Faggioli, ReTiS Lab, Scuola Superiore Sant’Anna, Pisa (IT) Real-Time Deadline Scheduling and More...