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VDM-RT Scheduling in Overture

VDM-RT Scheduling in Overture. Kenneth Lausdahl and Peter Gorm Larsen. Scheduling. Controls the available resources CPUs BUSses Deployment of instances of classes to cpus Inter-cpu communication implicitly over busses Schedule resources Advances time in time slices

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VDM-RT Scheduling in Overture

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  1. VDM-RT Scheduling in Overture Kenneth Lausdahl and Peter Gorm Larsen VDM-RT Scheduling

  2. Scheduling Controls the available resources CPUs BUSses Deployment of instances of classes to cpus Inter-cpu communication implicitly over busses Schedule resources Advances time in time slices Always determines minimum time slice to advance VDM-RT Scheduling 2

  3. Resources There is only one master scheduler Master scheduler is able to advance wall time VDM-RT Scheduling 3

  4. A Small Example system S instance variables cpu1 : CPU := new CPU(<FCFS>, 1E9); cpu2 : CPU := new CPU(<FCFS>, 1E9); static public a : A := new A(); static public b : B := new B(); operations public S: () ==> S S() == (cpu1.deploy(a); cpu2.deploy(b)) end S class Test operations public Run:() ==> nat * nat Run() == (start(S`a); start(S`b); return mk_(S`a.GetA(), S`b.GetB())) end Test class A instance variables a: nat := 0 operations public IncA: () ==> () IncA() == duration(6) a := a + 1; public GetA: () ==> nat GetA() == duration (10) (return a); sync per GetA => #fin(IncA) >= 1; mutex(IncA,GetA); thread for i = 1 to 3 do IncA() end A VDM-RT Scheduling 4

  5. Architecture BUS Resources CPU1 CPU2 vCPU Threads Threads Threads Policy Policy Policy … B A VDM-RT Scheduling 5

  6. Thread life cycle CREATED TIMESTEP Swap in/out RUNABLE • RUNABLE • Commit values from last run Swap in/out RUNNING RUNNING COMPLETED Swap out, kill Thread Policy controlsSwap VDM-RT Scheduling VDM-RT Scheduling 6 6 TIVDM2

  7. Schedule resource Resource Scheduler • Reschedule resource • Get thread through policy • Thread run time slice • RUNNING • If duration TIMESTEP • Else RUNABLE CPU1 Policy Threads CPU2 vCPU Threads Threads Policy Policy A … B Reschedule Reschedule VDM-RT Scheduling 7

  8. Time step size Cpu2 Cpu1 Time step size decided per thread in RUNNING stage Resource Scheduler uses smallest time step calculated over all resources. VDM-RT Scheduling

  9. Thread schedule on different cpus • A • i = 0 • RUNABLE • A • i = 0 • RUNNING • A • i = 0 • TIMESTEP(6) • A • i = 0 • TIMESTEP(4) • A • i = 0 • TIMESTEP(2) • A • i = 0 -> i = 1 • Committing last transaction • RUNNING … • B • i = 0 • RUNABLE • Reschedule • Time Step = 0 • B • i = 0 • RUNNING Reschedule • B • i = 0 • TIMESTEP(2) • B • i = 0 -> i = 1 • Committing last transaction • RUNNING Advance wall time.Time Step = min(2 ; 6) = 2 Reschedule • B • i = 1 • TIMESTEP(2) • B • i = 0 -> i = 2 • Committing last transaction • RUNNING Advance wall time.Time Step = min(2 ; 4) = 2 Reschedule • B • i = 2 • TIMESTEP(2) Advance wall time.Time Step = min(2 ; 2) = 2 • B • i = 0 -> i = 3 • Committing last transaction • RUNNING • B • i = 3 • COMPLETED … CPU1 CPU2 Scheduler VDM-RT Scheduling

  10. Thread schedule on the same cpu • A • i = 0 • RUNABLE • A • i = 0 • RUNNING • A • i = 0 • TIMESTEP(6) • A • i = 0 -> i = 1 • Committing last transaction • RUNNING … • Reschedule • Time Step = 0 • B • i = 0 • RUNABLE • B • i = 1 • RUNNING Compute thread in B Compute thread in A Compute thread in B Compute thread in B • B • i = 1 • TIMESTEP(2) Swap in thread A Advance wall time.Swap time Swap out thread A • B • i = 1 -> i = 2 • Committing last transaction • RUNNING Advance wall time.Swap time Swap in thread B Advance wall time.Swap time • B • i = 2 • TIMESTEP(2) • B • i = 2-> i = 3 • Committing last transaction • RUNNING Advance wall time.Time Step = 6 Advance wall time.Time Step = 12 Advance wall time.Time Step = 8 Advance wall time.Time Step = 10 Reschedule • B • i = 3 • TIMESTEP(2) • B • i = 3 -> i = 4 • Committing last transaction • RUNNING • B • i = 4 • COMPLETED … Both on CPU1 Scheduler VDM-RT Scheduling

  11. Scheduling Resources When the debug thread completes the execution is terminated. If all resources (CPUs and BUSes) are idle the model has deadlocked. VDM-RT Scheduling 11

  12. Reschedule CPUResource if (policy.reschedule()){ SchedulableThread best = policy.getThread(); if (running != best) // We swapped { If (running != null) RTLogger.log("ThreadSwapOut...); if (delayed) RTLogger.log("DelayedThreadSwapIn...); else RTLogger.log("ThreadSwapIn...); } running = best; running.runslice(policy.getTimeslice()); if (running.getRunState() == RunState.COMPLETE) { RTLogger.log("ThreadSwapOut...); RTLogger.log("ThreadKill...); running = null; } … • Reschedule of a CPU • VDM-RT Log • ThreadCreate • ThreadSwapIn • DelayedThreadSwapIn • ThreadSwapOut • ThreadKill… • Request • Activation • Completion • Of ops + messages VDM-RT Scheduling 12

  13. Threads @Override publicvoid run() { reschedule(); body(); setState(COMPLETE); resource.unregister(this); synchronized (allThreads) { allThreads.remove(this); } } abstract protected void body(); • One virtual thread (the debug thread) exists where duration is skipped. • All threads are implemented on top of Java threads • The abstract body will handle the actual execution of the thread. VDM-RT Scheduling 13

  14. Computation Step • public void step() • { • if (dialect is VDM_RT) • { • if (!virtual) // vCPUs don't take any time • duration(Properties.rt_duration_default); • } • else • SystemClock.advance(Properties.rt_duration_default); • if (++steps >= timeslice) • { • reschedule(); • steps = 0; • } • } When executing a computation step is taken before a time penalty is taken All Expressions and Statements have a default duration Can be overruled by cycle- and duration- statements VDM-RT Scheduling 14

  15. Async Operation Calls becomesThreads • Async operation calls on a different CPU goes over a BUS • Threads gets the parameter values through a message queue. • Gets parameter values as MessageRequest from BUS • Normal operation returns results as MessageResponse in the same BUS VDM-RT Scheduling 15

  16. BUS • Operation calls through a BUS • MessageRequest – ready to communicate • MessaggeActivate – Send the parameter values • MessageFinish – Take size of message into account in time penalty • MessageResponse – get the result • Data holder + ControlQueue • ControlQueue • A queue where threads can wait to get access • Block calls the waiting method of SchedulableThread • Get cannot complete before a reschedule • When guard potentially changes all threads are notified to recheck their blocked guards are now satisfied. VDM-RT Scheduling 16

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