Transcript What is the Linux Kernel?

Linux Kernel introduction
COSC 513
Xiaoping Yang
What is Linux
A clone of Unix operating system
Provides for the efficient management of system resources:
Linux is almost a freeware
First developed for 32-bit x86-based PCs (386 or higher).
Three major components:
Kernel
Shell Environment
File structure
What is the Linux Kernel?
The Heart of the Linux Operating System
Provides for the efficient management of system resources:
CPU
Interprocess Communication
Memory
Devices:
Disks
Terminals
Networks
Printers
What inside Linux Kernel
Linux Kernel is a monolithic kernel
Linux kernel Kernel contains:
System Call interface
Memory Manager
File System
Network support
Linux Processes and Tasks
Linux Process = Executing Program
Linux Task is a generalization of a Thread
Single threaded process is represented as a task
Multi-threaded process is multiple tasks
Only visible to the programmer and the kernel.
The Scheduler decides which task(s) gets to use the CPU(s)
Linux Scheduler
Multi-level queue scheduler
Three queues
SCHED_FIFO - standard priority.
Highest priority.
No time-slice
"supervisor" processes only
SCHED_RR - priority round robin.
Highest priority RR runs for 1 time slice.
"supervisor" processes only
SCHED_OTHER - time-sharing
All Linux user processes
Process Tree
There is a tree like relationship among processes:
Given the following:
$ netscape &
$ emacs &
$ xfig &
bash is the parent process
netscape, emacs and xfig are children of bash and
are siblings
netscape is the oldest sibling
xfig is the youngest sibling
Linux stores this structure as linked lists
Process Tree (cont.)
Task Tree
For every task the kernel maintains a task_struct
task_struct contains all relevant information
about a task.
General:
PID,Program name
Parent, youngest child, next sibling, previous sibling
Process Times (start_time, utime, stime,
cutime, cstime)
Scheduling algorithm, priority, nice value, errno
Process state
Owner:
UID
GID
Task tree (Cont.)
Files:
Information on all files opened by the process.
Stored in the fs_struct sub-structure
Memory:
Information about the memory used by a process.
IPC / Synchronization:
Pointers to acquired Semaphores
Bitmask of received Signals and associated Signal
handlers
Some other stuff...
Linux stores all task_structs in a doubly linked
list.
Linux Process State
Interrupts and System Calls
An interrupt is a request from the hardware for immediate
attention.
Two types of interrupts in Linux:
Fast Interrupts
Suspend current task, process interrupt, resume task
All other interrupts are generally disabled
Keyboard interrupt
Mouse interrupt
Interrupts and System Calls
(cont.)
Slow Interrupts
All registers are saved.
Only interrupts of same type are disabled.
Scheduler is called when ISR exits.
Timer interrupt
Disk Drive interrupt
System calls
Fast Interrupts in Linux
Suspend current task
Save CPU registers that might be altered
Switch CPU to kernel (system/supervisor/etc...) mode
Block all interrupts
Call Interrupt Service Routine (ISR)
Unblock interrupts
Switch CPU to user mode
Resume suspended task
Restore saved CPU Registers
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