Programmable Temporal Isolation in RealTime and Embedded
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Programmable Temporal Isolation in Real­Time and Embedded Execution Environments Silviu S. Crăciunaş, Christoph M. Kirsch, Hannes Payer, Harald Röck, Ana Sokolova University of Salzburg, Austria Outline RTOS Virtualization Microkernels Tiptoe design Scheduler Compact­fit memory management I/O Channels 2 / 13 RTOS Scheduling Static time slicing Priorities EDF No temporal isolation Protection single address space Co­located OS POSIX API or non standard API? Heterogeneous applications No spatial isolation 3 / 13 Virtualization Benefits Legacy software support Device driver Strict isolation Spatial isolation Embedded systems are highly integrated System VM is a black box – no control over threads Interdomain communication No temporal isolation 4 / 13 Microkernels Minimal software layer on top of hardware Fast IPC message passing Manages light­weight isolated components OS services and sensitive applications as servers Spatial isolation Protection Microkernel as hypervisor Type I hypervisor and paravirtualization L4Linux, OK­Wombat, ... No temporal isolation 5 / 13 tiptoe.cs.uni­salzburg.at 6 / 13 Temporal Isolation Process model Action is a piece of program code Process as sequence of actions Execution of an action is temporally isolated if the response time is determined by the code itself and its inputs independent of any concurrent activity 7 / 13 Scheduler Variable bandwidth servers (VBS) for individual process actions Generalization of constant bandwidth servers (CBS) Bandwidth cap (U) as percentage of CPU time Virtual periodic resource (,) Limit () Period () Processes dynamically adjust (,) U 8 / 13 Scheduler Process adjusts (,) to control its execution speed Programmable temporal isolation Response time variation (jitter) is at most Example: Controller loop with two actions Read Sensors, calculate, and update actuators low latency Update status, log state, send to terminal less stringent 9 / 13 Experiment 1=320, 3550 , 2=500,5340 10 / 13 Memory Management Compact­fit (CF) memory management [ATC'08] Allocator for object­based memory model Predictable in time and space Integration goal Processes specify allocation rate instead of CPU time Controlled by VBS scheduler 11 / 13 I/O Channels Communication link between two processes with a bandwidth cap Data transfer is like an action Data – workload Chunk size – limit Rate – period Integration goal Processes specify transfer rate of a data transfer Controlled by VBS scheduler 12 / 13 Q&A Thank you! 13 / 13
