1. MULTI-IMA PARTITION SCHEDULING
FOR GLOBAL I/O SYNCHRONIZATION
Jung Eun Kim, Man Ki Yoon, and Lui Sha
University of Illinois at Urbana-Champaign

2. Background
• Zero-partition has been used as a special-purpose ‘I/O partition’.
• In IMA, all I/O is consolidated in one zero-partition. Easy to manage.
• Synchronizing challenge among zero-partitions arise, when
migrating multiple single-core IMAs to a multi-core system.
• Ex. Shared device and shared I/O channel
• Supporting multiple rate groups is required.
• Partitions may not be harmonic in general.

3. Background
• Zero-partition has been used as a special-purpose ‘I/O partition’.
• In IMA, all I/O is consolidated in one zero-partition. Easy to manage.
• Synchronizing challenge among zero-partitions arise, when
migrating multiple single-core IMAs to a multi-core system.
• Ex. Shared device and shared I/O channel
• Supporting multiple rate groups is required.
• Partitions may not be harmonic in general.

4. Background
• Zero-partition has been used as a special-purpose ‘I/O partition’.
• In IMA, all I/O is consolidated in one zero-partition. Easy to manage.
• Synchronizing challenge among zero-partitions arise, when
migrating multiple single-core IMAs to a multi-core system.
• Ex. Shared device and shared I/O channel
• Supporting multiple rate groups is required.
• Partitions may not be harmonic in general.

5. A Solution – Serialized I/O Partitions
• Generate a Multi-IMA Schedule in which only one I/O
partitions runs at a time.
• Dedicated core (I/O core) for serializing I/O partitions
• As I/O partition running, other normal partitions can run concurrently.
• No application logic modification
• No additional certification cost

6. Physical I/O vs. Device I/O
• Physical I/O (P_I/O):
– Physical I/O for raw data between physical environment and I/O
device.
– Periodically operated at each I/O device.
• Device I/O (D_I/O):
– Device I/O. Buffered I/O. Between I/O device and DRAM.
– Scheduled as IMA partitions.
(e.g., device: camera, radar, sensor….;
raw data: temperature, pressure, radar signal…)
• We are using zero-partition for device I/O.

7. Physical/Device I/O Flows

8. Requirements on Partition Scheduling
• Precedence requirements:
P_I -> D_I -> processing partition -> D_O -> P_O
• Only one device I/O partition can (exclusively) run at a time.*
• Processing partitions on the same core must not be overlapped.

9. Assumptions
• A partition has its own device I/O partitions.
– Device I/O partitions are not shared.
• Processing partition and physical I/O: strictly periodic.
• Device I/O partitions: semi-periodic.
– Each invocation’s offset can vary at each minor frame
• Periods don’t need to be harmonic.

10. Partitions Schedule Generation
by Constraint Programming

11. Problem Description
• Input
– Lengths of physical I/O, device I/O, and processing
partitions.
– Periods of those partitions.
• Assume physical I/O periods are same with processing.
– Relative Deadline of device output.
• from the start of physical input
• Output
– Offsets of physical I/O, device I/O and processing
partitions.
• The whole multi-IMA schedule. (like a time table)

12. Example of Scheduled Partitions Overview

13. Example of Scheduled Partitions Overview

14. Example of Scheduled Partitions Overview

15. Example of Scheduled Partitions Overview

16. Example of Scheduled Partitions Overview

17. Practical Example
• IMA workload example
– Selectively made up from Generic Avionics Software Specification (SEI, 1990)

18. Practical Example
• IMA workload example
– Selectively made up from Generic Avionics Software Specification (SEI, 1990)

19. Result of Practical Example
• 1 I/O Core + 2 Processing cores; Periods (core_1: 40,200,100,100,100,40; core_2: 60, 40, 100); LCM=600
(magnified)
I/O core
(core 0)
core 1
core 2

20. Result of Practical Example
(magnified)
I/O core
(core 0)
core 1
core 2
• 1 I/O Core + 2 Processing cores; Periods (core_1: 40,200,100,100,100,40; core_2: 60, 40, 100); LCM=600

21. Extension
• Can be extended to add any “non-overlapping” constraints
– Ex: No simultaneous execution of
• specific or all Level-A partitions, specific or all high-bandwidth partitions
I/O core
(core 0)
core 1
core 2
Enforcement of
non-overlapping
between
Partition 5 and
Partition 8 I/O core
(core 0)
core 1
core 2

22. Summary
• IMA partition scheduling for synchronized I/O partitions
– Serializing on a dedicated core
• Can support multiple rate groups
• No application logic modification -> no additional certification cost
• More issues
– Multiple I/O devices
• Multiple I/O partitions can be on different cores if allowed to run
simultaneously.
• Can achieve a higher degree of parallelism.
– Inter-Partition communication
• Producer-Consumer. Some partitions may not need I/O partitions.
– Reassigning and relocating partitions
• The minimum number of required cores.
– Approximation algorithm
• CP can be slow with big inputs. Needs to develop a fast heuristic
algorithm.