CPU Scheduling Flashcards
Basis for multiprogrammed OS which maximises CPU utilization
CPU scheduling
Process execution which consists of a cycle of CPU execution and I/O wait
CPU burst (MAIN CONCERN) then I/O burst
CPU - I/O Burst Cycle
This selects from among the processes in the ready queue and allocates one of them in the CPU
Short term scheduler
CPU scheduling process takes place when a process
- switch from running to waiting
- switch from running to ready
- switch from waiting to ready
- terminate
(Nonpreemptive)
- consider access to shared data
- consider preemption while in kernel mode
- consider interrupts during crucial OS activities
(Preemptive)
Gives control of the CPU to the process selected by the short term scheduler which involves
- switching contexts
- switching to user mode
- jumping to proper location in the user program to restart
Dispatcher module
Time it takes for the dispatcher to stop one process and start another running
Dispatch latency
Scheduling criteria which keeps the cpu busy at all times
CPU utilization
Scheduling criteria which tracks the number of processes that complete their execution per time unit
Throughput
Scheduling criteria which is the amount of time for a process to execute a particular process
Turnaround time
Scheduling criteria which is the amount of time process has been waiting in the ready queue
Waiting time
Scheduling criteria which is the amount it takes from when a request has been passed until the first response is produced
Response time
A short process behind a long process
Convoy effect
Ho to determine length of next cpu burst
Exponential averaging
What is the problem of priority scheduling wherein LOW PRIORITY PROCESS MAY NEVER EXECUTE
Starvation
Solution to the problem of priority scheduling wherein as time progresses, increase the prirority of the process
Aging
A ready queue partitioned into ____ and ____
Multilevel queue
Foreground (interactive)
Background (batch)
Scheduling algo of foreground and background
RR ; fcfs
Scheduling between foreground and background
Fixed priority scheduling (foreground muna then background) Time slice (80% foreground in rr & 20% background)
Hierarchy of a multilevel queue scheduling
(Highest) system process Interactive process Interactive editing process Batch process Student process
A process can move between queues in this type of queue where in processes cn be demoted or promoted to different queues
Multilevel feedback queue
The thead library schedules USER LEVEL THREADS to run on lwp using PTHREAD_SCOPE _PROCESS
Process contention scope (local competition within process)
Kernel thread scheduled ontonavailable cpu using PTHREAD_SCOPE_SYSTEM
System contention scope (competition among all threads)
In a multiple processor scheduling, only one processor accesses the system data structures increasing the need for data sharing
Asymmetric multiprocessing
In a multiple processor scheduling, each processor is self scheduled wherein all processes in common ready queue has its own private queue pr ready processes
Symmetric multiprocessing (smp)
Types of processor affinity
Soft and hard affinity
Valiations incluing PROCESSOR SETS
A way to keep efficiency of the CPU in SMP whrein trying to mainti=ain eben distributi9oon
Load balancing
In smp, periodic tasks checks load on each processor and pushes task from overload cpu to other cou
Push migration
In smp, idle processor pulls waiting task from busy processor
Pull migration
A recent trend to place multiple processor cores on the same PHYSICAL CHIP which is FASTER AND CONSUMES LESS POWER
And multiple cores per thread also grows.
Execute another thread while memory stall is happening
Multicore processor
A type of cpu scheduling where it can present obvious challenges
Real time cpu scheduling
A type of realmtime cpu scheduling whrein there is no guarantee as tonwhen critical reak time process will be scheduled
Soft real time systems
Task must be servicd by the deadline
Hard real time system
A type of latency from ARRIVAL OF INTERRUPT to START OF ROUTINE that service the interrupt
Interrupt latency
A type of latency which is the time for schedule to TAKE CURRENT PROCESS and SWITCH to another
Dispatch latency
Priorities are assugned based in deadlines
Earliest deadline first (edf) scheduling
How to select CPU scheduling algrithm for an os
Determine criteria and evaluate algorithm
A type of ANALYTICAL EVAUATION wherein it takes a predetermined workloa and defines performance of each algorithm for that workload
Deterministic modeling
