Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems DS-RT 2019, Cosenza Italy, 2019-10-08 Jalil Boudjadar 1 Saravanan Ramanathan 2 and Arvind Easwaran 2 Ulrik Nyman 3 ulrik@cs.aau.dk 1 Aarhus University, Denmark 2 Nanyang Technological University, Singapore 3 Distributed, Embedded and Intelligent Systems, DEIS Department of Computer Science Aalborg University, Denmark
Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Setting and Purpose 1 Mixed-critical systems ◮ High criticality tasks ( HC ) ◮ Low criticality tasks ( LC )
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Setting and Purpose 1 Mixed-critical systems ◮ High criticality tasks ( HC ) ◮ Low criticality tasks ( LC ) ◮ HC tasks should never miss a deadline ◮ Dropping as few LC tasks as possible
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Related Work 2 Two approaches System-level mode ◮ Two system modes ◮ Normal ◮ Critical Task-level mode
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Related Work 2 Two approaches System-level mode ◮ Two system modes ◮ Normal ◮ Critical ◮ Drop all LC tasks ◮ Run LC tasks in degraded mode Task-level mode
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Related Work 2 Two approaches System-level mode ◮ Two system modes ◮ Normal ◮ Critical ◮ Drop all LC tasks ◮ Run LC tasks in degraded mode Task-level mode ◮ Each HC task switches individually to Critical
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Related Work 2 Two approaches System-level mode ◮ Two system modes ◮ Normal ◮ Critical ◮ Drop all LC tasks ◮ Run LC tasks in degraded mode Task-level mode ◮ Each HC task switches individually to Critical ◮ Other HC tasks can miss their deadline
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Assumptions 3 ◮ Tasks are preemptible. ◮ All tasks are assigned a static criticality level (LC or HC) by design, called default criticality. ◮ The execution of a HC task must not be discarded under any runtime circumstances. ◮ The runtime criticality of a LC task can never be upgraded to HC. ◮ LC tasks stick always to their low confidence WCET. ◮ There is no dependency between LC and HC tasks.
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Task 4 A task π i is given by � T i , C l i , C h i , χ i , ρ � where: ◮ T i is the task period. ◮ C l i ∈ R ≥ 0 and C h i ∈ R ≥ 0 are the worst case execution time for low and high confidence levels respectively. We assume that C h i ≥ C l i for HC tasks, and C h i = C l i for LC tasks. ◮ χ i ∈ { LC , HC } is the default (constant) criticality of the task. ◮ ρ is the task priority. The task runtime mode Ω() will be updated on the fly according to the actual task execution budget.
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Task types 5 ◮ Types of tasks HC LC Type High criticality Low criticality Modes HI and LO no modes Varies C h i ≥ C l Static C h i = C l WCET i i
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Task types 5 ◮ Types of tasks HC LC Type High criticality Low criticality Modes HI and LO no modes Varies C h i ≥ C l Static C h i = C l WCET i i ◮ Modes for HC tasks HI LO C h C l WCET i i
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Three scheduling functions 6 Sched : 2 Π × R ≥ 0 → Π ◮ Fixed priority scheduling ◮ Intermediate scheduling Sched I (Π , t ) = π i | Ready ( π i , t ) ∧ ∀ π j ∈ Π Ready ( π j , t ) ⇒ Ω( π j , t ) < Ω( π i , t ) ∨ Ω( π j , t ) = Ω( π i , t ) ∧ Sched ( { π i , π j } , t ) = π i ◮ Critical scheduling Sched C (Π , t ) = π i | Ready ( π i , t ) ∧ ∀ π j ∈ Π Ready ( π j , t ) ⇒ χ j < χ i ∨ ( χ j = χ i ) ∧ Ω( π j , t ) < Ω( π i , t ) ∨ ( χ j = χ i ) ∧ (Ω( π j , t ) = Ω( π i , t )) ∧ Sched ( { π i , π j } , t ) = π i
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems System scheduling mode behavior 7 Workload (when all HC tasks Normal run C h ) exceeds Threshold Critical mode mode At least one HC task terminated
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Example 8 Simple mixed task set C l C h Task T χ ρ 20 5 7 HC 2 π 1 20 5 6 HC 4 π 2 20 5 - LC 1 π 3 20 4 - LC 3 π 4
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Example 9 Runtime example for the system in Table C l overrun Ω=LPLO π1 ρ =LP 2 Ω=LPHI Ω=LPLO ρ =LP 4 π2 ρ =LP 1 π3 π4 ρ =LP 3
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Low criticality task behavior 10 System scheduling-mode switched to Critical Active Active Period (stretched (regular) stretching period) Active (shrunk period) Period shrinking
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems High criticality task behavior 11 WCET C l violation Active Active (LO mode) (HI mode) Period termination
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Example of LC task periods shrinking 12 Shrinking with ∆ =12 over interval[5,30] Critical System mode: Normal 5 HI mode 30 HC task π 1 : LO mode (T=30,C=7) 7 Stretching 35 LC task π 2 : Regular µ =6 21 (T=20, C=4) Shrinking Stretching LC task π 3 : µ =4 Regular (T=14,C=3) Shrinking 38 8 18 28
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Algorithm 13
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Case study 14 Origin ◮ Task set from [14] R. Dodd. Coloured petri net modelling of a generic avionics missions computer. Technical report, Department of Defence, Australia, Air Operations Division, 2006. ◮ WCET ( C l ) given in original case. ◮ WCET ( C h ) calculated from data fetching times. ◮ 20 µ s for data words ◮ 40 µ s for a command ◮ 40 µ s for a status
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Case study 15 Tasks C l C h Task T χ ρ Aircraft flight data( π 1 ) HC 55 8 8.9 6 Steering( π 2 ) HC 80 6 6.3 9 Target tracking( π 3 ) HC 40 4 4.2 3 Target sweetening( π 4 ) HC 40 2 2 4 AUTO/CCIP toggle( π 5 ) HC 200 1 1 12 Weapon trajectory( π 6 ) HC 100 7 7.5 10 Reinitiate trajectory( π 7 ) LC 400 6.5 - 14 Weapon release( π 8 ) HC 10 1 1.2 1 HUD display( π 9 ) LC 52 6 - 7 MPD tactical display( π 10 ) LC 52 8 - 8 Radar tracking( π 11 ) HC 40 2 2.2 2 HOTAS bomb button ( π 12 ) LC 40 1 - 5 Threat response display( π 13 ) LC 100 3 - 11 Poll RWR( π 14 ) LC 200 2 - 13 Perodic BIT( π 15 ) LC 1000 5 - 15
Jalil Boudjadar Saravanan Ramanathan and Arvind Easwaran Ulrik Nyman ulrik@cs.aau.dk | Combining Task-level and System-level Scheduling Modes for Mixed Criticality Systems Case Study 16 Uppaal model
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