Linux Process (Task) Structure and Scheduling Overview

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Linux Process (Task) Structure and Scheduling
Overview

• CS3013 C02
• Jae Chung Hariharan Kannan

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Process Control Block (PCB)

• Process is called Task in Linux
• PCB struct task_struct
• Essentials pid, state, stack, files,
  semaphore
• Task Ment next_task, prev_task, ptree,
• Task Sched priority, counter, next_run,
  prev_run
• Resource Usage times, maj_flt, min_flt, nswap
• And more

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Task Managements
Task Tree (All Tasks)
Task List (All Tasks)
Run Queue (Ready Tasks)
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Linux Scheduler Functions

• (Previous process give up CPU)
• Handles interrupts (latter half)
• Select next process (task) to run
• Performs context switch if necessary
• (Let go the next process selected)

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Linux Process Scheduling

• Normal Credit-Based (counter variable)
• process with most credits is selected
• goodness() 0 (if counter 0)
• goodness() counter priority (otherwise)
• Timer goes off (jiffy, 1 per 10 ms)
• then lose a count (0, then suspend)
• No runnable process (all suspended)
• reload (recalculate) counter value
• counter counter/2 priority
• Real-Time goodness() 1000 rt_priority

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Kernel Source Files to Start

• /usr/src/linux/include/linux/sched.h
• /usr/src/linux/kernel/sched.c
• /usr/src/linux/kernel/sys.c (getrusage)
• /usr/src/linux/kernel/fork.c (fork)