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UNIVERSIDADDE CANTABRIA
Modeling and schedulability analysis of AFDX networks in MAST 2
J. Javier Gutiérrez ([email protected])
Computers and Real-Time Group, University of Cantabriawww.ctr.unican.es
Funded in part by Spanish Government and FEDER funds(TIN2011-28567-C03-02-HI-PARTES)
1st Workshop on Real-Time Ethernet (RATE)Vancouver (Canada), December 2013
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 1UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Introduction to MAST
MAST (Modeling and Analysis Suite for Real-Time Applications)• is a long-term project led by Michael González Harbour
• defines a model to describe the timing behavior of distributed real-time systems
• model supports different scheduling policies, and is used by different tools- schedulability analysis- sensitivity analysis- assignment of scheduling parameters- simulation
Available at http://mast.unican.es
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 2UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Overview of the MAST model
Real-time situation view
Platform view
EventHandler
Step
TimingRequirement
Operation
MutualExclusion
SchedulableResource
Scheduler
SchedulingParameters
Event Event
Event
Reference
ProcessingResource
Operations view
Concurrent architecture view
Resources
StepEvent
End-to-end flow
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 3UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Evolution to MAST 2
The MAST model is now aligned with the model defined in MARTE• the standardized UML profile for real-time embedded systems
MAST 2 also includes new modeling elements
• network switches and routers- IEEE 802.1p switches with prioritized traffic- ARINC-664 standard (part 7): a hard real-time network known as
AFDX (Avionics Full-Duplex Switched Ethernet)
• network links: AFDX elements and communication channels
• timetable-driven scheduling- allows modeling partitioned systems based on ARINC-653
standard
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 4UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Main characteristics of AFDX
Switched ethernet network• based on the use of point to point full duplex ethernet links
• and special purpose switches
• UDP/IP protocol is used for transmission
The routing of messages is preconfigured
• there is no delay in the discovery of routing addresses
Traffic regulation at the sending end via Virtual Links (VL)
The switches have two FIFO queues at each output port
• high and low priority traffic
• the priority is configured on a VL basis
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 5UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Virtual Links
Each VL has two parameters• Lmax: the largest Ethernet frame in bytes
• BAG: the Bandwidth Allocation Gap (BAG)- a power of 2 in the range [1,128] ms- the BAG is the minimum interval between Ethernet frames
transmitted on the VL
Each virtual link has a FIFO queue for all the fragmented packets to be transmitted through it
A virtual link can be composed of up to 4 Sub-Virtual Links
• a dedicated FIFO queue per sub-VL
• a round robin algorithm working over IP fragmented packets
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 6UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
The AFDX architecture
END SYSTEM
VL1 Queue
VLn Queue
...VL Scheduler
Transmitting AFDX Section
High Priority Queue
Low Priority Queue
AFDX Switch Output PortAFDX Switch
END SYSTEM END SYSTEM
END SYSTEM
AFDX Switch
SWITCHED NETWORK
of an End System
Sub-VLm Queue
...Sub-VL1 QueueRR Sched.
VL Q.
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 7UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Networks in MAST 2
Network
Packet_Based_Network
Transmission_KindMax_Packet_SizeMin_Packet_SizeMax_Blocking
Driver
0..* Driver_List
Processing_Resource
Clock_Synchronization_Object
0..1 Synchronization_SourceSpeed_Factor
Throughput
RTEP_Network
...
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 8UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
AFDX networks
Network
Packet_Based_NetworkDriver
0..* Driver_ListThroughput
AFDX_Link
Max_Packet_SizeMin_Packet_SizeMax_HW_Tx_LatencyMax_W_Rx_LatencyEhernet_OverheadProtocol_Oerhead
Also Min, Avg
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 9UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
AFDX Virtual Links
Scheduling_Parameters
...
AFDX_Virtual_Link
Lmax : Bit_CountBAG : Time
Schedulable_Resource
...
Communication_Channel
0..1
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 10UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Network switches and routers
Network_Switch
Processing_Resource
Clock_Synchronization_Object
0..1 Synchronization_SourceSpeed_Factor
Max_Fixed_Fork_Latency
AFDX_Switch
...
Max_Variable_Fork_LatencyMax_Delivery_Latency
Also Min, Avg
Regular_Switch
...Network_Router
Max_Fixed_Branch_LatencyMax_Variable_Branch_Latency
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 11UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
A simple example
Sender Data Receiver
CPU1 CPU2AFDX Switch
Task TaskMessage
Data
Ethernet
Message
Data
Ethernet
Message
SenderData Receiver
CPU1 CPU2AFDX Network
Task TaskMessage
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 12UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Modeling the AFDX network
Real-Time situation view
Platform view
Concurrent architecture view
Net_Sched2: Primary_Scheduler
Policy = AFDX_Policy
...
Net_Sched: Primary_Scheduler
Policy = AFDX_Policy
...
M2: Fixed_Priority_Params
Priority = 1
...
Switch: AFDX_Switch
Max_Delivery_Latency = 10e-6
...
Stream1: Communication_Channel
...
Stream2: Communication_Channel
...
M1: AFDX_Virtual_Link
LMax = 1200
BAG = 4e-3
Link1: AFDX_Link
TThroughput = 1e8
...
Link2: AFDX_Link
TThroughput = 1e8
...Host Host
Scheduling_Parameters
Step_Schedulable_Resource
Scheduler
Step_Schedulable_Resource
Sw itchScheduler
Scheduling_Parameters
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 13UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Modeling the AFDX network (cont’d)
Real-Time situation view
Operations view
M2: Fixed_Priority_Params
Priority = 1
...
Stream1: Communication_Channel
...
Stream2: Communication_Channel
...
M1: AFDX_Virtual_Link
LMax = 1200
BAG = 4e-3
Data: Message
Max_Message_Size = 1600
...
MD: Message_Delivery
...
E22: Internal_Event
...
E23: Internal_Event
...
E2: Internal_Event
...
E3: Internal_Event
...
S2: Step
...
S1: Step
...
Output_Event
Step_Operation
Input_Event
Scheduling_Parameters
Output_Event
Step_Schedulable_ResourceStep_Schedulable_Resource
Step_Operation
Input_Event
Input_Event
Output_Event
Scheduling_Parameters
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 14UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
MAST for schedulability analysis
The MAST model is transformed into internal models for schedulability analysis or simulation based on the end-to-end flow• processors and networks are treated in a similar way
i1
ei i2 i3
di2Di2
Di3=Di
CPU-1 CPU-2Network
i2
Ji3
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 15UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Schedulability analysis for heterogeneous systems
A holistic analysis can be applied by dealing with each step separately• fixed priorities or EDF (either with local or global clocks) can be mixed in the same distributed system
ij
Pij SDij | Sdij
Rbij
Rijij
Jij
Activation conditions
Scheduling parameters
Response times
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 16UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Holistic schedulability analysis technique for AFDX
Can be integrated in the analysis for heterogeneous systems• calculates the worst-case and the best-case latencies, and thus the output jitter
• manages multipacket messages and input jitter
• useful for multicast messages and multiple switches with any number of priority levels (2 for AFDX switches)
• includes the analysis of VLs and sub-VLs
Recently published online in the Real-Time Systems Journal
Compatible with a new analysis technique for ARINC-653 systems (to be published soon)
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 17UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Validation of the technique
The analysis technique is an adaptation of the holistic analysis initially developed by Tindell and Clark• it is well known that this analysis is pessimistic
Obtains results
• similar to other techniques, e.g., Network Calculus
• less accurate than the Trajectory approach
• but these techniques consider the network in isolation and work over a more simplified model
It is scalable and can be applied to real systems
• exact calculation of latencies (e.g., model-checking) is intractable except for small systems
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 18UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Results for a real size example
Architecture:• 16 switches
• 1000 VLs crossing up to 6 switches
0
10
20
30
40
50
60
70
80
90
14 19 24 28 33 38 42 47
Executiontim
e(s)
Average output ports utilization (%)
Avg. Exec. Time
Max. Exec. Time
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 19UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Current state and future of MAST 2
The model has been defined and formulated in Ecore (Eclipse/EMF) as part of a model-driven strategy to enable• model transformations for analysis or simulation
We have developed the analysis techniques for ARINC-like partitioned systems with AFDX networks
We also have a lot of work to do to implement all of this
• strong changes are needed in the current implementation to continue to guarantee compatibility
We want to explore new analysis techniques to reduce the pessimism
• applying offsets or adapting the Trajectory approach
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 20UNIVERSIDAD DE CANTABRIA 3/Dec/13
UNIVERSIDADDE CANTABRIA
Questions?
http://www.percivalconstantine.com/wp-content/uploads/2013/02/wip.png
GRUPO DE COMPUTADORES Y TIEMPO REAL By: J. Javier Gutiérrez 21UNIVERSIDAD DE CANTABRIA 3/Dec/13