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Polling server

The document outlines various challenges faced by Harish Chetty while working on an EDF polling server, including dealing with extensive code and multiple system failures. Key concepts discussed include task scheduling, deadline management, and performance issues with kernel compilation and task execution. It also touches on data structures used like RB trees and max heaps for efficient task handling.

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EDF POLLING SERVER Harish Chetty
Lots of Problems! • Had to read about 20,000 Lines of Code Spread across 7 unrelated files. • Had to read through 2000 more lines to interpret Mark’s Sporadic server! • Understood about 20% code (which I thought was 80% at the beginning). • Reinstalled Kernel about 500 Times. • Found out limitations of printk’s! • Some crash caused Disk(or something to corrupt) forcing use of TTY. • SMP’s made life hell. • CBS ensured PS to always fail! • Finally the last phase was carried out on kernel which took 20 minutes to compile. • HAD TO FINALLY UNDERSTAND ABOUT 50% TO GET STUFF DONE!
IMAGINE A CLOCK! Rings Bell Every 60 Seconds Period : 60 sec Must Ring Bell for 5 Seconds Budget: 5 sec Complete Ringing in 10 Second Deadline: 10 sec
Submit Task Setup Deadline & Budget Enqueue Task Dequeue Task Budget Exhausted Budget Left When the task must end! How much time the task should run? ? Task Dead TASK COMPLETE/KILL KILL Wakeup task, Run the task, Update Runqueues etc. Schedule task, Block the task, Push task in wating queue etc.
Submit Task Setup Deadline (D), Budget (B) & Replenishment Timer (RT) Enqueue Task Dequeue Task B = Cap RT Timeout B = 0 ? Task Dead TASK COMPLETE/KILL KILL INIT Task Release Replenishment Timer (RT)
Submit Task Setup(D), (B) & (RT) Enqueue Task Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = Cap B = Cap B = 0 CPU RUNQUEUE TIME INITIAL BUDGET Release (RT)
Submit Task Setup(D), (B) & (RT) Enqueue Task Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B = Cap B = Cap B = 0 Release (RT)
Submit Task Setup(D), (B) & (RT) Enqueue Task Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B >= Cap B = Cap B = (0 + P) OVERRUN TIME (Penalty (P)) Release (RT)
WHAT IF MORE THAN ONE TASK? WHAT IF MORE THAN ONE TYPE OF TASK?
SCHED_OTHER (CFS) SCHED_RT SCHED_DEADLINE BATCH IDLE NORMAL EDFFIFO ROUND ROBIN IDLE TASK SCHED_POLL 99 to 0132 to 100> 132 -1 -2
Submit Task Setup(D), (B) & (RT) Enqueue Task P = -2 Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B >= Cap B = Cap B = (0 + P) Release (RT)
Submit Task Setup(D), (B) & (RT) Enqueue Task P = -2 Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B >= Cap B = Cap B = (0 + P) Release (RT) Forward RQ TIME == Deadline! D = D + D Why NOT 2D ?? Here comes Periods!
WHAT IF MORE THAN ONE CPU?
Submit Task Setup(D), (B) & (RT) Enqueue Task P = -2 Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B >= Cap B = Cap B = (0 + P) Release (RT) Forward RQ TIME == Deadline! D = D + D SMP Enqueue Task P = -2 SMP Dequeue Task RT Timeout B = 0 B = (0 + P) N(CPU) > 1
Submit Task Setup(D), (B) & (RT) Enqueue Task P = -2 Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B >= Cap B = Cap B = (0 + P) Release (RT) Forward RQ TIME == Deadline! D = D + D SMP Enqueue Task P = -2 SMP Dequeue Task RT Timeout B = 0 B = (0 + P) N(CPU) > 1 Select CPU
WHAT IF MORE THAN ONE SCHED_POLL TASK?
Submit Task Setup(D), (B) & (RT) Enqueue Task P = -2 Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B >= Cap B = Cap B = (0 + P) Release (RT) Forward RQ TIME == Deadline! D = D + D SMP Enqueue Task P = -2 SMP Dequeue Task RT Timeout B = 0 B = (0 + P) N(CPU) > 1 Select CPU Pick Next Task Preempt verifier
volatile long long int count =0; while(1){ if(count<1000000){ count++; printf("Printing number %lld n", count); } else{ break; } }
I WILL STOP BORING YOU AND END!
EXTRAS
Data Structures • Pick Next Tasks use RB Trees based on Deadlines. • Leftmost Node is cached (smallest Deadline) • CPU’s work using Max Heaps based on task deadlines. • Root Node has CPU with a task with the largest Deadline. Preempt this first if necessary • Must be a Queue for more efficiency?? • Waiting Tasks use RB Trees based on Deadlines. • Leftmost Node is cached (smallest Deadline)
Submit Task Setup Deadline & Budget Enqueue Task Dequeue Task Budget Left = 0 Budget Left != 0 When the task must end! How much time the task should run? ? Wakeup task, Run the task, Update Runqueues etc. Schedule task, Block the task, Push task in wating queue etc.
Submit Task Setup(D), (B) & (RT) Enqueue Task P = -2 Dequeue Task B = (RQ TIME – START TIME) RT Timeout B = 0 Task Dead TASK COMPLETE/KILL KILL INIT Task Task Running Update Status B = 0 / B >= Cap B = Cap B = (0 + P) Release (RT) Forward RQ TIME == Deadline! D = D + D SMP Enqueue Task P = -2 SMP Dequeue Task RT Timeout B = 0 B = (0 + P) N(CPU) > 1 Select CPU Pick Next Task