CS6200 Final Exam Review Part 3 - Scheduling Lesson 1

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Who is the author of the CS6200 Final Exam Review guide?

An Udacity instructor

A current student

A professor

George Kudrayvtsev (correct)

What is the purpose of the formula 'derivations' in the context of scheduling metrics?

To calculate the completion time of tasks

To determine the queueing order of tasks

To generalize and understand each metric better (correct)

To compare scheduling algorithms

What does the variable Ti represent in the context of scheduling metrics?

The completion time of task i (correct)

The queueing order of task i

The execution time of task i

The number of tasks used for the metric

What is the ideal scenario for determining the completion time of tasks?

When the task completion time is known prior to execution Signup and view all the answers

What is the variable n used to represent in the context of scheduling metrics?

The number of tasks used for the metric Signup and view all the answers

What is the primary goal of considering various metrics when discussing scheduling?

To compare the performance of different scheduling algorithms Signup and view all the answers

When is it beneficial to context switch between tasks?

When 2t < context switch < tblocking task Signup and view all the answers

What is the purpose of a scheduler in scheduling tasks?

To minimize the overhead of the interruption and algorithm Signup and view all the answers

Why are longer timeslices beneficial for CPU-bound tasks?

They enable the task to make the most of its CPU time Signup and view all the answers

What is the advantage of shorter timeslices for I/O-bound tasks?

They enable the task to respond to user requests Signup and view all the answers

What is the purpose of the multi-level feedback queue?

To dynamically balance a task's timeslice based on its history Signup and view all the answers

What happens when a task yields voluntarily during its given timeslice?

It belongs at that timeslice level Signup and view all the answers

What was the problem with the O(1) scheduler that led to the development of the CFS?

It did not dynamically balance a task's timeslice Signup and view all the answers

What is the average completion time for the tasks T1, T2, and T3?

11.4 s Signup and view all the answers

What is the CPU utilization for the tasks T1, T2, and T3?

82% Signup and view all the answers

What is the average wait time for the tasks T1, T2, and T3?

1.833 s Signup and view all the answers

What is the primary function of the vruntime in task scheduling?

To adjust the running time of tasks based on their priority Signup and view all the answers

What is the time complexity of selecting a task in the scheduling algorithm?

O(1) Signup and view all the answers

What is the metric proposed by Fedorova to measure the 'average instruction delay'?

CPI (Cycles Per Instruction) Signup and view all the answers

What is the purpose of the 'dirty bit' in a page table entry?

To indicate whether a page has been written to since it was loaded Signup and view all the answers

What happens when a process tries to access a page not present in physical memory?

A page fault occurs and the OS handles it Signup and view all the answers

What is the purpose of page tables in memory management?

To translate virtual addresses to physical addresses Signup and view all the answers

How does the OS map the memory allocated to a process to the underlying physical memory?

Using a page table Signup and view all the answers

What is the role of the Memory Management Unit (MMU) in page tables?

To perform the translation between virtual and physical addresses Signup and view all the answers

What is the purpose of the 'accessed bit' in a page table entry?

To indicate whether a page has been accessed during some period of time Signup and view all the answers

What happens when a translation for a requested address is present in the page table but does not translate to an existing physical memory address?

The data is moved from the disk to physical memory. Signup and view all the answers

What is the purpose of the 'copy-on-write' optimization in page tables?

To allow multiple virtual address spaces to refer to the same physical pages. Signup and view all the answers

What is the result of an unintended unallocated access, such as dereferencing an invalid pointer?

A segmentation fault is triggered and sent to the user process. Signup and view all the answers

Why is the 'not allowed' type of access critical for certain exploitation prevention techniques?

It prevents unauthorized access to certain memory regions. Signup and view all the answers

What is the purpose of the access bit in the page table?

To determine which page to replace in the page table. Signup and view all the answers

What is the result of a process accessing a page that is not in physical memory?

The MMU issues a page fault to the operating system. Signup and view all the answers

What is the purpose of demand paging?

To simulate a larger address space than is physically available. Signup and view all the answers

What is the role of the page replacement policy in demand paging?

To decide which page to replace in the page table. Signup and view all the answers

What is the purpose of the dirty bit in the page table?

To track which pages have been modified. Signup and view all the answers

How many entries does the second table have in the given memory addressing schema?

4 Signup and view all the answers

What address space does a single inner-most page table address in the context given?

64MiB of memory Signup and view all the answers

In the memory addressing schema discussed, how many layers are there in total?

16 Signup and view all the answers

What does the parameter P3 index into in the given address chunking sequence?

The third table Signup and view all the answers

How many bits are used for the offset in the virtual address chunking in the provided context?

12 bits Signup and view all the answers

What does the Avg. Job Wait Time measure?

The time it takes for a task to move from the 'queued' state to the 'executing' state Signup and view all the answers

What is the definition of CPU Utilization?

The percentage of time that the CPU is using to do 'useful work' Signup and view all the answers

How is Avg. Job Completion Time calculated for a FCFS policy?

$\frac{1}{n}\sum_{i=1}^{n}(n-i+1)Ti$ Signup and view all the answers

What is the primary purpose of understanding the derivation of the scheduling formulas rather than memorizing them?

To synthesize the information for complex scenarios Signup and view all the answers

What triggers the scheduling algorithm to execute periodically?

All of the above Signup and view all the answers

What does the CPU Utilization measure?

The percentage of time the CPU is doing 'useful work' Signup and view all the answers

For Average Job Completion Time with SJF policy, what replaces Ti in the formula for FCFS?

Cj Signup and view all the answers

What is the primary reason for placing importance on understanding the derivation of scheduling formulas?

To synthesize information for more complex scenarios Signup and view all the answers

What data structure is closely associated with scheduling algorithms to enable specific decision-making?

Runqueue Signup and view all the answers

What is the purpose of having a consistent, recurring interval for calculating CPU Utilization?

To measure the percentage of useful work in small intervals Signup and view all the answers

In the Linux O(1) scheduler, what indicates a non-empty index in the array used for task selection?

First set bit in a bitmap Signup and view all the answers

What is the range of priorities for tasks in the Linux O(1) scheduler?

0 to 99 Signup and view all the answers

What happens when the timeslice of a task expires in the Linux O(1) scheduler?

The task is moved to the expired array Signup and view all the answers

What is the main data structure used in the Linux CFS Scheduler?

Red-Black Tree Signup and view all the answers

How is a task's priority adjusted based on its idle time in the Linux O(1) scheduler?

Inversely proportional Signup and view all the answers

What is vruntime in the Linux CFS Scheduler proportional to?

Time spent by a task on the CPU Signup and view all the answers

How does the Solaris scheduler handle I/O-bound tasks noticing a task yields often for its timeslice?

Increases the timeslice Signup and view all the answers

Why did the O(1) scheduler become unacceptable as workloads changed?

It caused unpredictable scheduling times Signup and view all the answers

What is the key difference between higher and lower priority tasks in the Linux O(1) scheduler?

Higher priority tasks have lower priority values Signup and view all the answers

How does the Linux CFS scheduler ensure fairness among tasks?

By using a red-black tree for task ordering Signup and view all the answers

In address translation, the purpose of the Translation Lookaside Buffer (TLB) is to:

Translate virtual addresses to physical addresses quickly. Signup and view all the answers

What is the role of page table entries in address translation?

Correlate virtual page numbers to physical page numbers. Signup and view all the answers

How does splitting a virtual address into multiple levels of page tables benefit memory management?

Minimizes wasted space in page tables. Signup and view all the answers

What is the purpose of discretizing virtual addresses into virtual page numbers (VPNs)?

To index into a page table. Signup and view all the answers

What is the relationship between address space and the physical memory size in address translation?

The address space is independent of physical memory size. Signup and view all the answers

How does the page size influence the size of a page table?

Larger page size leads to larger page tables. Signup and view all the answers

What happens in address translation after a virtual address is indexed into a page table?

The offset is concatenated with the physical address. Signup and view all the answers

Why is hierarchical page table structure preferred for memory management?

To reduce unnecessary page table entries and gaps. Signup and view all the answers

What purpose does the Translation Lookaside Buffer (TLB) serve in the context of address translation?

It speeds up address translation by caching page table entries. Signup and view all the answers

What is the significance of the physical memory size in relationship to page table calculations?

It is a crucial factor in calculating the required page table entries. Signup and view all the answers