Module 1:
Process Management and Scheduling
Introduction to the Linux kernel, Process Management – Process, Process
descriptor and the task structure, Process creation, The Linux implementation of
threads, Process termination. Process Scheduling – Multitasking, Linux’s process
scheduler, Policy, Linux scheduling algorithm, Preemption and context switching,
Real-time scheduling policies.
Linux Kernel
The Linux kernel serves as the core component of the Linux operating system,
responsible for managing hardware resources, providing essential services to
user-space programs, and facilitating communication between software and
hardware components. This includes process management, memory
management, file systems, device drivers, and networking protocols. Each of
these components plays a crucial role in the overall functionality and
performance of the operating system.
Process management is responsible for creating, scheduling, and terminating
processes, allowing multiple programs to run concurrently on the system.
Memory management ensures efficient utilization of system memory by
allocating and deallocating memory resources as needed. File systems provide a
hierarchical structure for organizing and accessing data stored on storage
devices, such as hard drives and SSDs.
Device drivers act as intermediaries between hardware devices and the kernel,
allowing the kernel to communicate with various hardware components,
including storage devices, network interfaces, and input/output devices.
Networking protocols enable communication between different computers over a
network, facilitating tasks such as file sharing, remote access, and internet
connectivity.
Process- process Management
Process management in the Linux kernel is a crucial aspect of its functionality,
facilitating the creation, scheduling, and termination of processes.
Process Creation:
,When a program is executed, the Linux kernel creates a corresponding process
to manage its execution. This process is represented by a data structure known
as the process control block (PCB) or task_struct in Linux.
Process creation involves initializing various attributes of the process, including
its process ID (PID), parent process ID (PPID), state, memory space, and
execution context.
The fork() system call is commonly used to create new processes in Linux. This
call duplicates the calling process, resulting in the creation of a new child
process.
Process Scheduling:
Process scheduling is the mechanism by which the Linux kernel decides which
process to execute on the CPU at any given time.
The Linux scheduler employs various scheduling policies, such as the Completely
Fair Scheduler (CFS) and the Real-Time (RT) scheduler, to manage the execution
of processes.
Scheduling decisions are based on factors such as process priority, CPU
utilization, and scheduling policy parameters.
Process States:
Processes in Linux can exist in several states, including:
Running: The process is currently executing on the CPU.
Waiting: The process is waiting for a specific event or resource, such as I/O or
synchronization.
Stopped: The process has been paused or stopped, often due to a signal or
debugger intervention.
Zombie: The process has terminated, but its exit status has not yet been
collected by its parent process.
The Linux kernel transitions processes between these states based on their
execution status and resource requirements.
Process Termination:
Process termination occurs when a process completes its execution or explicitly
calls the exit() system call to terminate itself.
Upon termination, the Linux kernel releases the resources associated with the
process, including memory, file descriptors, and other system resources.
,If the terminated process has child processes, the kernel ensures that they are
properly re-parented to an appropriate process.
Process Descriptor:
The process descriptor, often referred to as "struct task_struct," is a crucial data
structure in the Linux kernel that represents a process.
It contains detailed information about the process, including its state, scheduling
parameters, memory management information, file descriptors, signal handlers,
and various other attributes.
The process descriptor is dynamically allocated for each process when it is
created and is stored in kernel memory.
This data structure is used by the kernel to manage and control the execution of
the process, including scheduling decisions, resource allocation, and
synchronization.
Task Structure:
The task structure is synonymous with the process descriptor in the Linux kernel
and is represented by the "struct task_struct" data type.
It serves as the primary data structure for representing processes and threads in
the kernel, encapsulating all the necessary information about a process.
The task structure contains fields such as process ID (PID), parent process ID
(PPID), process state, scheduling information, signal handlers, and pointers to
other kernel data structures.
Additionally, the task structure is used by various subsystems within the kernel
to access and manipulate process-related information, such as memory
management, file system operations, and interprocess communication.
Process Descriptor and the Task Structure
The kernel stores the list of processes in a circular doubly linked list called the
task list. Each element in the task list is a process descriptor of the type struct
task_struct, which is defined in <linux/sched.h>. The process descriptor contains
all the information about a specific process.
Some texts on operating system design call this list the task array. Because the
Linux implementation is a linked list and not a static array, it is called the task
list.
, The task_struct is a relatively large data structure, at around 1.7 kilobytes on a
32-bit machine. This size, however, is quite small considering that the structure
contains all the information that the kernel has and needs about a process. The
process descriptor contains the data that describes the executing programopen
files, the process's address space, pending signals, the process's state, and
much more
Process Descriptor and the Task Structure
The kernel stores the list of processes in a circular doubly linked list called
the task list[3]. Each element in the task list is a process descriptor of the
type struct task_struct, which is defined in <linux/sched.h>. The process
descriptor contains all the information about a specific process.
Some texts on operating system design call this list the task array. Because
[3]
the Linux implementation is a linked list and not a static array, it is called
the task list.
The task_struct is a relatively large data structure, at around 1.7 kilobytes on a
32-bit machine. This size, however, is quite small considering that the structure
contains all the information that the kernel has and needs about a process. The
process descriptor contains the data that describes the executing programopen
files, the process's address space, pending signals, the process's state, and
much more (see Figure 3.1).
Figure 3.1. The process descriptor and task list.
Process Management and Scheduling
Introduction to the Linux kernel, Process Management – Process, Process
descriptor and the task structure, Process creation, The Linux implementation of
threads, Process termination. Process Scheduling – Multitasking, Linux’s process
scheduler, Policy, Linux scheduling algorithm, Preemption and context switching,
Real-time scheduling policies.
Linux Kernel
The Linux kernel serves as the core component of the Linux operating system,
responsible for managing hardware resources, providing essential services to
user-space programs, and facilitating communication between software and
hardware components. This includes process management, memory
management, file systems, device drivers, and networking protocols. Each of
these components plays a crucial role in the overall functionality and
performance of the operating system.
Process management is responsible for creating, scheduling, and terminating
processes, allowing multiple programs to run concurrently on the system.
Memory management ensures efficient utilization of system memory by
allocating and deallocating memory resources as needed. File systems provide a
hierarchical structure for organizing and accessing data stored on storage
devices, such as hard drives and SSDs.
Device drivers act as intermediaries between hardware devices and the kernel,
allowing the kernel to communicate with various hardware components,
including storage devices, network interfaces, and input/output devices.
Networking protocols enable communication between different computers over a
network, facilitating tasks such as file sharing, remote access, and internet
connectivity.
Process- process Management
Process management in the Linux kernel is a crucial aspect of its functionality,
facilitating the creation, scheduling, and termination of processes.
Process Creation:
,When a program is executed, the Linux kernel creates a corresponding process
to manage its execution. This process is represented by a data structure known
as the process control block (PCB) or task_struct in Linux.
Process creation involves initializing various attributes of the process, including
its process ID (PID), parent process ID (PPID), state, memory space, and
execution context.
The fork() system call is commonly used to create new processes in Linux. This
call duplicates the calling process, resulting in the creation of a new child
process.
Process Scheduling:
Process scheduling is the mechanism by which the Linux kernel decides which
process to execute on the CPU at any given time.
The Linux scheduler employs various scheduling policies, such as the Completely
Fair Scheduler (CFS) and the Real-Time (RT) scheduler, to manage the execution
of processes.
Scheduling decisions are based on factors such as process priority, CPU
utilization, and scheduling policy parameters.
Process States:
Processes in Linux can exist in several states, including:
Running: The process is currently executing on the CPU.
Waiting: The process is waiting for a specific event or resource, such as I/O or
synchronization.
Stopped: The process has been paused or stopped, often due to a signal or
debugger intervention.
Zombie: The process has terminated, but its exit status has not yet been
collected by its parent process.
The Linux kernel transitions processes between these states based on their
execution status and resource requirements.
Process Termination:
Process termination occurs when a process completes its execution or explicitly
calls the exit() system call to terminate itself.
Upon termination, the Linux kernel releases the resources associated with the
process, including memory, file descriptors, and other system resources.
,If the terminated process has child processes, the kernel ensures that they are
properly re-parented to an appropriate process.
Process Descriptor:
The process descriptor, often referred to as "struct task_struct," is a crucial data
structure in the Linux kernel that represents a process.
It contains detailed information about the process, including its state, scheduling
parameters, memory management information, file descriptors, signal handlers,
and various other attributes.
The process descriptor is dynamically allocated for each process when it is
created and is stored in kernel memory.
This data structure is used by the kernel to manage and control the execution of
the process, including scheduling decisions, resource allocation, and
synchronization.
Task Structure:
The task structure is synonymous with the process descriptor in the Linux kernel
and is represented by the "struct task_struct" data type.
It serves as the primary data structure for representing processes and threads in
the kernel, encapsulating all the necessary information about a process.
The task structure contains fields such as process ID (PID), parent process ID
(PPID), process state, scheduling information, signal handlers, and pointers to
other kernel data structures.
Additionally, the task structure is used by various subsystems within the kernel
to access and manipulate process-related information, such as memory
management, file system operations, and interprocess communication.
Process Descriptor and the Task Structure
The kernel stores the list of processes in a circular doubly linked list called the
task list. Each element in the task list is a process descriptor of the type struct
task_struct, which is defined in <linux/sched.h>. The process descriptor contains
all the information about a specific process.
Some texts on operating system design call this list the task array. Because the
Linux implementation is a linked list and not a static array, it is called the task
list.
, The task_struct is a relatively large data structure, at around 1.7 kilobytes on a
32-bit machine. This size, however, is quite small considering that the structure
contains all the information that the kernel has and needs about a process. The
process descriptor contains the data that describes the executing programopen
files, the process's address space, pending signals, the process's state, and
much more
Process Descriptor and the Task Structure
The kernel stores the list of processes in a circular doubly linked list called
the task list[3]. Each element in the task list is a process descriptor of the
type struct task_struct, which is defined in <linux/sched.h>. The process
descriptor contains all the information about a specific process.
Some texts on operating system design call this list the task array. Because
[3]
the Linux implementation is a linked list and not a static array, it is called
the task list.
The task_struct is a relatively large data structure, at around 1.7 kilobytes on a
32-bit machine. This size, however, is quite small considering that the structure
contains all the information that the kernel has and needs about a process. The
process descriptor contains the data that describes the executing programopen
files, the process's address space, pending signals, the process's state, and
much more (see Figure 3.1).
Figure 3.1. The process descriptor and task list.
