Operating System Learning notes (5)

Swap technology, Exchange technology:
(swapping)
In order to free up memory space, swap out/swap in process (program or data, PCB can not be swapped out).

Reason for the pending state of the process:
-Process blocking All
-Heavy system load and tight memory space.
-the needs of the operating system.
-The end user's request.
-The requirements of the parent process.

Characteristics of the suspended process:
1. Cannot execute
2. May wait for a time to occur (selecting a pending process may be a blocked process)
3. The process to suspend is: itself, parent process, OS

Suspend and block
Problem:
1. Whether the blocking process can only be suspended.
2. How to activate the suspend process.
Differentiate between two concepts: "Wait Time"-block "swap out memory"-pending

Two additional states:
Ready/Pending
Blocking/suspending

Note:
There are two types of processes that can be scheduled to be executed by the processor:
1. The newly created process
2. Swap in a previously suspended process


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Control of the process:

Two modes of execution:
1. System mode/control mode/kernel mode
-With high privileges
-System-specific instructions
-processor machine instructions, registers, and memory are fully controlled and protected
1. User mode
-Low privilege
-User Program


Mode switch:
User-System: System call
System-User: Execute system call
Special case: End of program, no longer returned to user mode


System Kernel (Kernel)
1. Hardware-based first-tier software expansion is the basis of operating system work.
2. Hardware-related, basic, public, high-frequency modules, and critical data structures are independent of the memory. have higher privileges.
3. System calls are implemented through the system kernel.
4. Kernel function: Resource management function and support function.

Resource features:
1. Process Management
2. Storage function
3. IO Device Management


Support function:
1. Terminal processing
2. Clock management
3. Primitive Language (Primitive): Atomic manipulation
4. Statistics
5. Monitoring


Process Control Primitives:
1. Process switching
2. Create and terminate
3. Blocking and Awakening
4. Suspend and activate


Process creation: Reason
1. Submit a new batch job
2. Interactive User Registration
3. Operating system provides tasks
4. Parent process creates child process

Process creation: Steps
1. Assign a unique flag number ID to a process terminate
2. Allocating space for a process
3. Initialize PCB
4. Establish links
5. Create or extend other data structures

Process termination: Reason
1. Execute to "end" statement
2. Interactive User "Logoff"
3. Stop the execution of a process
Specific causes: Normal end, timeout, out of memory, access out of bounds, calculation error, timeout wait event
IO failure, invalid instruction, privileged instruction, data type mismatch, etc.

Process termination: Step
1. Terminate ID, find PCB, read status
2. Terminating a child process
3. Process resource restitution system (or parent process)
3. Move the PCB

Blocking and waking of processes:
Block primitive, wake up primitive language

Pending and activation of the process:
Suspend primitive, activate primitive language

Process switching:
Clock interrupt
IO Interrupt
Access error
Trap

Process a switches to step B:
1. Protection process A field to PCB inside
2. Recovery process B on-site

Process switching vs Mode switching:
Process switching-"CPU conversion" must trigger a mode switch because the process switch must have a "system call". otherwise.
Mode Switch-"system call"



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Process scheduling:

What is dispatch.
In a queue, according to a certain algorithm, select a suitable individual process.

Scheduling target:
Fairness, processor utilization, increased system throughput, reduced process response time

Scheduling principle:
Meet the user's requirements
Meet the needs of the system

User-oriented principle: Response time
Evaluate the performance of time-sharing systems.

User-oriented principle: Cycle time
Evaluate the performance of batch processing systems.
Job scheduling, process scheduling, medium-range scheduling (hangs)

User-oriented principle: deadline
1. The latest time a task must perform, or the latest time it must complete, in a real-time system.
2. Evaluate the performance of real-time systems.

System-oriented principles: decency throughput

System-oriented principles: Processor utilization

System-oriented principles: balanced use of all types of resources

System-oriented principles: fairness

System-oriented principles: priority