Klara Nahrstedt Spring 2011 CS 414 – Multimedia Systems Design Lecture 32 – Process Management (Part 2) Klara Nahrstedt Spring 2011 CS 414 - Spring 2011

Administrative MLC application ‘mi-clicker’ is published on the Android Market under “MLC Edu App”. Check the class website for a document “Getting Started” with the mi-clicker!!! Starting Monday, we will use the phones at the beginning of each class, so bring phones to the class. CS 414 - Spring 2011

Outline EDF vs RMS Dynamic Soft Real Time Scheduling CPU service classes Probing concept Overrun- adaptation concept CS 414 - Spring 2011

Admission Control (for preemptive tasks) Schedulability test for RMS Schedulability test for EDF CS 414 - Spring 2011

Example Consider the following preemptive RT tasks and their characteristics T1: p1 = 50ms, e1=10ms T2: p2 = 100ms, e2=20ms T3: p3 = 200ms, e3=50ms T4: p4 = 100ms, e4=20ms Are these tasks schedulable via RMS? If yes, what is the feasible schedule? Are these tasks schedulable via EDF? CS 414 - Spring 2011

DSRT (Dynamic Soft Real-Time Scheduling) – Example of a Multimedia CPU Scheduler Multiple CPU Service Classes Schedule real-time and not real-time tasks in an integrated fashion Execution Flow of a SRT Process Possible Mapping CPU Service Classes into a Multiprocessor Partitioning Design Source: Hao-hua Chu 1999 CS 414 - Spring 2011

CPU Service Classes Service Classes Specification Parameters Guaranteed PCPT (Periodic Constant Processing Time) P = Period PPT = Peak Processing Time PPT PVPT (Periodic Variable Processing Time) P = Period SPT = Sustainable Processing Time PPT = Peak Processing Time BT = Burst Tolerance SPT ACPU (Aperiodic Constant Processor Utilization) PPU PPU = Peak Processor Utilization Relative Deadline PPT = Peak Processing Time Event PPT CS 414 - Spring 2011

Periodic Constant Processing Time Class Example Usage Pattern: Peak Processing Time=10ms Period = 100ms 10 110 210 100 200 Time(ms) Processing IIIIIIIIIII frames CS 414 - Spring 2011

Periodic Variable Processing Time Class Example Usage Pattern: Period = 100ms Peak Processing Time = 30ms Sustainable Processing Time = 15ms Burst Tolerance = 7ms 15 120 210 100 200 Time(ms) Processing of IPBBPI frames CS 414 - Spring 2011

Execution Flow of a SRT Process Probing Phase Execution Phase Reservation Phase Scheduling Probe Admission Control Extract Reservation Monitor/ Conformance Test Contract Processor Binding Adaptation SRT Process Adjusted Contract CS 414 - Spring 2011

C++ APIs CpuApi cpu; CpuReservation reservation; // Probing Phase; cpu.probe(); cpu.start(); for (int i=0; i<numProbeIterations; i++) { doJob(); cpu.yield(); } cpu.stop(); cpu.probeEnd(); cpu.probeMatch(&reservation); // Reservation Phase cpu.reserve(reservation); cpu.setAdaptStrategy(strategy); // Execution Phase cpu.start(); for (;;) { doJob(); cpu.yield(); } cpu.stop(); cpu.free(); CS 414 - Spring 2011

Smart Offline Probing (1) Goal: Extract a reservation. Determine the most suitable Service Class and Parameters. Avoid over/under reserve resources. Needed because: Processor usage is hardware platform dependent. Processor usage is input dependent. CS 414 - Spring 2011

Smart Probing (2) DSRT runs a few iterations of SRT applications without reservation. DSRT monitors the usage iteration by iteration. DSRT analyzes the usage history. Estimate a Reservation Processor Usage Iteration Number CS 414 - Spring 2011

Smart Probing (3) It is Periodic Variable Processing Time (PVPT) Compute average processor usage = 50ms Compute peak processor usage = 62ms. Max Burst = 12ms It is Periodic Variable Processing Time (PVPT) 40ms 50ms 62ms 43ms 55ms 12ms 40ms 50ms 62ms 55ms 60ms 10ms 5ms 50ms 50ms 50ms 50ms 50ms

Multiprocessor Partitioning Design Guaranteed Part Non-guaranteed Part PCPT Processes Reserved Run Overrun PVPT Processes Reserved Run Burst Overrun TS Processes RT Scheduler Overrun Scheduler TS Scheduler Processor #1 RT Partition Overrun Partition TS Partition Processor #2 RT Partition Overrun Partition TS Partition CS 414 - Spring 2011

Admission Control Test Given a reservation request, determine Resource Availability. (1) + (2) Processor Binding. (2) Preemptive Earliest Deadline First: CS 414 - Spring 2011

Partition Scheduling Processor #1 RT Partition Overrun Partition Top-Level Scheduler Proportional Sharing RT Scheduler Overrun Scheduler TS Scheduler Multi-Level Round Robin Priority Queues Preemptive EDF Kernel Scheduler Processor #1 RT Partition Overrun Partition TS Partition Processor #2 RT Partition Overrun Partition TS Partition CS 414 - Spring 2011

RT Partition Scheduler Processor #1 Waiting Queue: (Sorted with the earliest released time) p (2a) finished one iteration (3) released for next iteration p (1) admitted p Runnable Queue: (Sorted with the earliest deadline) (2b) overrunning Overrun Partition Queues CS 414 - Spring 2011

Overrun Partition Scheduler Highest Priority Burst Queue (FIFO) (2) Miss Deadline p (1a) Conformed? Overrun Queue (FIFO) (1b) Nonconformed? p Permanent Non-conforming Queue (FIFO) (1c) Nonconformed frequently? Lowest Priority CS 414 - Spring 2011

Adaptation Adjust Reservation. Adaptive Strategy Exponential Average Scene #1 Scene #2 Adjust Reservation. Adaptive Strategy Exponential Average CS 414 - Spring 2011 Frame 275

Exponential Average Adaptation Strategy ... Xws-1 Xws Xws+1 ... X2ws ... X3ws Iteration Number Adaptation Points Specification: Window Size (ws). Alpha () Xi= Guaranteed Parameter in a reservation. Xi-1 = Actual Usage. CS 414 - Spring 2011

User-level Priority Dispatch Highest Priority (5) Dispatched Process runs for T ms. (4) Scheduler sleeps. Fixed RT Priority (3) Scheduler sets Timer for T ms. N DSRT Scheduler Process (6) Timer interrupts Scheduler N-1 Dispatched Process . ....... (2) Set Processor Affinity. ....... . Time Sharing Processes (5) Decrease Priority . ....... (1) Increase Priority. Dynamic TS Priority ....... RT Process Pool Lowest Priority CS 414 - Spring 2011

Experiment Setup Run 8 TS processes and 5 SRT processes concurrently. TS1-6: Computational intensive programs. TS7-8: Compilation programs. SRT1: A MPEG player at 10 FPS. Probing (PVPT class, P=100ms, SPT=28ms, PPT=40ms, BT=11ms). Adaptation Strategy: (Statistical, f = 20%, ws = 20). CS 414 - Spring 2011

Experimental Setup (Cont.) SRT2: A MPEG player at 20 FPS. Probing (PVPT class, P=50ms, SPT=14ms, PPT=21ms, BT=6ms) SRT3: A sampling program. Probing(PCPT class, P=50ms, PPT=10ms) SRT4: A Java RocksInSpace game. (PCPT class, P=100ms, PPT=30ms). SRT5: Misbehaving greedy program. (PCPT class, P=500ms, PPT=10ms). CS 414 - Spring 2011

Experimental Result SRT2: MPEG player with P=50ms. CS 414 - Spring 2011

Experimental Result (Cont.) SRT3: Sampling program with P=50ms. SRT4: Java game with P=100ms. CS 414 - Spring 2011

Conclusion (Over-provisioning Approach) Current Approach: To achieve throughput - overprovision of resources (fast processors, large disks, fast I/O bus, high-speed networks), and exclusive usage of resources To achieve timing - overprovision CPU, exclusive usage of resources, application-dependent scheduling Current Thesis: With over-provisioning we get Quality of Service !! CS 414 - Spring 2011

Conclusion (Problems with Over-provisioning) Violation of Timing Guarantees in Exclusive Case (head-of-line blocking) Sensory and Video Data Processing/Transmission Violation of Timing/Throughput Guarantees in Shared Case (greedy applications, flows) UDP flows versus TCP Flows Last Mile Problem (not everywhere is over-provisioning possible) Telescopes, University Campus Need support of QoS in OS towards multimedia tasks CS 414 - Spring 2011