Lesson 3: Process Management Flashcards
unit of work in most systems
Process
program in execution; process execution must progress in sequential fashion
Process
set of associated resources
Process
Examples of Processes
Compiler
Word processor
Email program
Sending output to a printer
T or F: Although 2 processes may be associated with the same program, they are considered 2 separate execution sequences.
True
What does a process include? (PSDT)
Program counter
Stack
Data Section
Text Section
[What does a process include] specifies the next instruction to be executed
Program counter
[What does a process include] contains temporary data
Stack
[What does a process include] contains global variables
Data section
[What does a process include] program code
Text section
Representation of a process in the operating system
PCB
What does PCB stand for?
Process Control Block
[PCB] Different states as a process executes (NRRWT)
New
Ready
Running
Waiting
Terminated
[Process State] the process is being created
New
[Process State] The process is waiting to be assigned to a processor
Ready
[Process State] Instructions are being executed
Running
[Process State] The process is waiting for some event to occur
Waiting
[Process State] The process has finished execution
Terminated
[PCB] contains the memory address of the next instruction to be executed for this process
Program counter
[PCB] CPU registers include: (ASIG)
Accumulators
Stack Pointers
Index Registers
General Purpose Registers
[PCB] Memory-management information includes: (VPS)
Value of base and limit registers
Page tables
Segment tables
[PCB] I/O Status information includes
list of I/O devices allocated to this process, list of open files, etc.
[PCB] CPU scheduling information includes: (PPS)
Process priority
Pointers to scheduling queues
Scheduling Parameters
[PCB] Accounting information includes (RLAJ)
Amount of CPU and REAL TIME used
Time LIMITS
Account numbers
Job or process number, etc.
Process Scheduling Queues (JRD /jared/)
Job queue
Ready queue
Device queues
[Process Scheduling Queues] set of all processes in the system
Job queue
[Process Scheduling Queues] set of all processes residing in main memory, ready and waiting to execute
Ready queue
[Process Scheduling Queues] set of processes waiting for an I/O device
Device queues
Schedulers (LS)
Long-term scheduler (job scheduler)
Short-term scheduler (CPU scheduler)
[Schedulers]
—selects which processes should be brought into the ready queue
—invoked very infrequently
—controls the degree of multiprogramming
Long-term scheduler (job scheduler)
[Schedulers]
—selects which process should be executed next and allocates CPU.
—invoked very frequently
Short-term scheduler
Processes can be described as either: (IC)
I/O-bound process
CPU-bound process
[Bound Processes] spends more time doing I/O than computations, many short CPU bursts
I/O-bound process
[Bound Processes] spends more time doing computations; few very long CPU bursts
CPU-bound processes
[Schedulers]
—an intermediate level queue used in systems with virtual memory or timesharing
—removes processes from the memory and reintroduced later (swapping)
—reduces the degree of multi programming
Medium term
[Process States, New] 4 principal events for process creation (SERI)
System initialization
Execution of a process creation system call by a running process
A user REQUEST to create a new process
Initiation of a batch job
set of all processes in the system
Job queue
selects which processes should be brought into the ready queue.
Long-term scheduler (job scheduler)
When is job scheduling done?
If there is not enough room in the main memory for all processes in the job queue
[Process States, Ready] contains set of all processes residing in main memory, ready and waiting to execute
Ready queue
selects which process should be executed (dispatched) next and allocates CPU
Short-term scheduler (CPU scheduler)
a module that gives control of the CPU to the process selected by the short-term scheduler
Dispatcher
[Process States, Running] events that may occur while process is being executed (RESR)
—issues an I/O REQUEST and then be placed in an I/O queue.
—The time slice allotted to the process in CPU has EXPIRED
—creates a new SUBPROCESS (forks a child) and waits for its termination.
—forcibly REMOVED from the CPU as a result of an interrupt and then be placed back in the ready queue
[Process States, Terminated] Process terminates are due to: (NEFK)
Normal exit (voluntary)
Error exit (voluntary)
Fatal error (involuntary)
Killed by another process (involuntary)
When does waiting or blocked state becomes suspended
when swapped to disk to free up more memory
When does waiting or blocked state becomes suspended
when swapped to disk to free up more memory
Additional states (R, BW, BS, RS)
Ready – process in main memory and available for execution
Blocked/Waiting – process in main memory and awaiting an event
Blocked/Suspend – process in secondary memory and awaiting an event
Ready/Suspend – process in secondary memory and available for execution
Three states once a process is created (RRB)
Ready
Run
Blocked
Reasons for a process to be blocked (MILT)
MESSAGE: Waiting for a message from another process
I/O: Waiting for I/O completion
LOAD: Waiting for the code to be fully loaded in memory
TIME: Waiting for a particular time of day
Transitions (DBWP)
Dispatch
Block
Wakeup
Preempt
Transition from READY to RUN
Dispatch
transition from RUN to BLOCKED
Block
transition from BLOCKED to READY
Wakeup
transition from RUN to READY
Preempt
Two types of process termination (NA)
Normal
Abnormal
process termination due to a call by the process to a termination statement
Normal termination
the forced termination of the process by the OS due to some unrecoverable error such as bound violation, arithmetic error, and invalid instruction
Abnormal termination
—Responsible for allocating the CPU among various ready processes in the system
—Usually called after an interrupt has been served
—Ask the job scheduler for the process most suitable to take control of the CPU
Dispatchers
[Schedulers] Selects form among those READY processes in memory
Short-term scheduler (CPU Scheduler)
[Schedulers] Determines which jobs are admitted to the system
Long-term scheduler (job scheduler)
Long-Term Scheduling Properties (EMASP)
Expected runtime
Maximum memory size
Amount of I/O
Special resources required (tape, disk)
Priority/deadlines
Short-Term Scheduling Algorithms (P, NP)
Preemptive
Non-preemptive
[CPU Scheduling]
—Scheduling strategy where the CPU is suspended when a higher priority process is in the ready queue
—Currently running process may be interrupted and moved to the ready state by the operating system
—Allows for better service since any one process cannot monopolize the processor for very long
Preemptive
[CPU Scheduling]
—Scheduling strategy where even if a higher priority process is ready, the running process is allowed to continue until either it is blocked or completes its execution
—Once a process is in the running state, it will continue until it terminates or blocks itself for I/O
Non-preemptive
time it takes for the dispatcher to stop one process and start another running
Dispatch latency
[CPU Scheduling] The process that requested the CPU first is allocated first
First-Come First-Served Scheduling (FCFS)
[CPU Scheduling] Is FCFS preemptive or non-preemptive?
Non-preemptive
[CPU Scheduling] Scheduling is done thru the next CPU burst rather than the total length of the process
Shortest Job First (SJF)
[CPU Scheduling] Is SJF preemptive or non-preemptive?
Both (preemptive is SRTF or Shortest Remaining Time First)
[CPU Scheduling]
—A priority number (integer) is associated with each process
—The CPU is allocated to the process with the highest priority
Priority Scheduling
[Priority Scheduling] Rule in priority scheduling
Smallest integer has highest priority
[CPU Scheduling] Is Priority Scheduling preemptive or non-preemptive?
Both (non-preemptive = NPP, preemptive = PP)
[CPU Scheduling]
—time slicing
—designed especially for time-sharing systems
—similar to FCFS, but preemption is added to switch between process
Round Robin (RR)
[CPU Scheduling] Is Round Robin preemptive or non-preemptive?
Preemptive
[CPU Scheduling] Process with the highest response ratio is executed next
Highest-Response-Ratio-Next (HRRN)
[CPU Scheduling] Is HRRN preemptive or non-preemptive?
Non-preemptive
[CPU Scheduling] How is response ratio computed?
(Waiting time + burst time)/burst time
[CPU Scheduling]
—Ready queue is partitioned into separate queues
—Jobs are permanently assigned to 1 queue
—Each queue has its own scheduling algorithm
Multi-Level Queue (MLQ)
[CPU Scheduling] A process can move between the various queues; aging can be implemented this way
Multilevel Feedback Queue (MLFQ)
