RT OS
and
RT Linux
Daniel Bristot de Oliveira
Who I'm and what we will

talk about?
an Operating

System overview
Application

Operating System

Hardware
Tasks of an OS
Hardware...
Embedded system without OS
OS as a library
OS as a library
OS as a library
Memory Protection - MMU
OS with a Micro-Kernel
OS as we know
What does Real-Time
means?
Event -> Response,
latency,

response time,

deadline...
Real-Time means
fast?
Real Time != FAST!
RT

means

Determinism,
WCET,
Response Time.
What is a Real-Time

Operating System?
Deterministic hardware
+
Deterministic hardware abstraction
+
Services with WCET
+
Deterministic Resource Management
=
?
Real-Time Operating

System Examples
?
FreeRTOS
Neutrino (QNX)
Linux ?
Why

is Linux not a
RTOS?
Linux is too much flexible
General Purpose OS
●

●

Linux not is a RTOS by conception
Higher throughput rather than higher
determinism.
●

●

High la...
Linux as a RTOS?
●

Why?

●

Hardware support
●

●

Services
●

●

ARM, MIPS, POWERPC, intel, TILE 64, ADBF...
FS, Network...
How

Red Hat shows your Real-Time
Linux
Real-Time Linux: Past,

Present, Possible
Futures...
RTAI and Xenomai
RT Task on Xenomai
+
Non-RT on Linux...

=
):)

<- this is a bipolar emoticon
PREEMPT-RT
- latency
+ control over OS tasks
Sources of latency
●

IRQ Handling
●

●

Preempt off
●

●

Softirq
spinlocks

IRQ off
Preemptive lock
Priority inversion
problems...
IRQ Handling
How good is PREEMPT_RT Today?
PREMPT-RT is

WONDERFULL!

Let's use everywhere!!!
)

:)

This is another bipolar emoticon, but more happy
than another...
How expensive is
PREEMP-RT?
50
45
40
35

CPU Load (%)

30
PREEMPT-RT
Vanilla

25
20
15
10
5
0
12

24

36
Concurrent channels

60
LITMUS

RT
A testbed for multiprocessor

scheduling

in Real-Time Systems
(Partitioned|Global|Clustered) EDF
Partitioned Fixed-Priority
PD2 (PFAIR)
Mutual Exclusion
Interrupt Handling
Real-Time GPU Management
Tracing Tools
How good is Litmus RT?
Litmus RT
=
a way to pick next task
with a RT API.
A little bit of my MS Degree dissertation...
Questions?
2013 ufsc rt_grad_class
2013 ufsc rt_grad_class
2013 ufsc rt_grad_class
2013 ufsc rt_grad_class
2013 ufsc rt_grad_class
2013 ufsc rt_grad_class
2013 ufsc rt_grad_class
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2013 ufsc rt_grad_class

  1. 1. RT OS and RT Linux Daniel Bristot de Oliveira
  2. 2. Who I'm and what we will talk about?
  3. 3. an Operating System overview
  4. 4. Application Operating System Hardware
  5. 5. Tasks of an OS
  6. 6. Hardware...
  7. 7. Embedded system without OS
  8. 8. OS as a library
  9. 9. OS as a library
  10. 10. OS as a library
  11. 11. Memory Protection - MMU
  12. 12. OS with a Micro-Kernel
  13. 13. OS as we know
  14. 14. What does Real-Time means?
  15. 15. Event -> Response, latency, response time, deadline...
  16. 16. Real-Time means fast?
  17. 17. Real Time != FAST!
  18. 18. RT means Determinism, WCET, Response Time.
  19. 19. What is a Real-Time Operating System?
  20. 20. Deterministic hardware + Deterministic hardware abstraction + Services with WCET + Deterministic Resource Management = ?
  21. 21. Real-Time Operating System Examples
  22. 22. ?
  23. 23. FreeRTOS
  24. 24. Neutrino (QNX)
  25. 25. Linux ?
  26. 26. Why is Linux not a RTOS?
  27. 27. Linux is too much flexible
  28. 28. General Purpose OS ● ● Linux not is a RTOS by conception Higher throughput rather than higher determinism. ● ● High latency. But has: ● Static priority sched: FIFO and RR
  29. 29. Linux as a RTOS? ● Why? ● Hardware support ● ● Services ● ● ARM, MIPS, POWERPC, intel, TILE 64, ADBF... FS, Network Stack... Money ● Rich company X needs a low latency Oracle database.
  30. 30. How Red Hat shows your Real-Time Linux
  31. 31. Real-Time Linux: Past, Present, Possible Futures...
  32. 32. RTAI and Xenomai
  33. 33. RT Task on Xenomai + Non-RT on Linux... = ):) <- this is a bipolar emoticon
  34. 34. PREEMPT-RT
  35. 35. - latency + control over OS tasks
  36. 36. Sources of latency ● IRQ Handling ● ● Preempt off ● ● Softirq spinlocks IRQ off
  37. 37. Preemptive lock
  38. 38. Priority inversion problems...
  39. 39. IRQ Handling
  40. 40. How good is PREEMPT_RT Today?
  41. 41. PREMPT-RT is WONDERFULL! Let's use everywhere!!!
  42. 42. ) :) This is another bipolar emoticon, but more happy than another...
  43. 43. How expensive is PREEMP-RT?
  44. 44. 50 45 40 35 CPU Load (%) 30 PREEMPT-RT Vanilla 25 20 15 10 5 0 12 24 36 Concurrent channels 60
  45. 45. LITMUS RT
  46. 46. A testbed for multiprocessor scheduling in Real-Time Systems
  47. 47. (Partitioned|Global|Clustered) EDF Partitioned Fixed-Priority PD2 (PFAIR)
  48. 48. Mutual Exclusion Interrupt Handling Real-Time GPU Management Tracing Tools
  49. 49. How good is Litmus RT?
  50. 50. Litmus RT = a way to pick next task with a RT API.
  51. 51. A little bit of my MS Degree dissertation...
  52. 52. Questions?

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