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School of Engineering and Technology June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma
Beyond Physical Memory,
Review for “Final” Quiz
Wes J. Lloyd
School of Engineering and Technology
University of Washington - Tacoma TCSS 422: OPERATING SYSTEMS This is a “cloud computing” course Previous year’s course: http://faculty.washington.edu/wlloyd/courses/tcss Course introduces major cloud computing delivery models: Infrastructure-as-a-Service (IaaS), Platform (PaaS), Functions (FaaS), Container (CaaS), Software (SaaS) Course features a software development project where we build and evaluate software entirely for the cloud Topics: introduction to major cloud services, developing ser verless software (Function-as-a-Service), containerization FALL 2021 - TCSS 562 SOFTWARE ENG. FOR CLOUD COMPUTING June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19.
School of Engineering and Technology
Class does not have prerequisites
TCSS 422 provides good foundation – we use Linux
If interested in enrolling, contact by email
Can take 1 x 500-level class, counts as 400-level elective
SAVINGS: able to take graduate course and only pay
undergraduate tuition
DOUBLE-DIP !!
Class taken in last quarter of undergrad can be used twice
Once as a undergraduate elective towards graduation Once as a graduate elective towards the Masters in Computer Science & Systems (MSCSS) degree June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. TCSS 562 – CLOUD COMPUTING - 2 Independent study in “cloud computing” Work to collaboratively draf t a proposal and submit to Dr. Nascimento, CSS Chair F 2021 for approval Focus on variety of topics related to cloud/distributed systems Variable credits from 1 to 5 Involves par ticipation in weekly research group meeting Spring 2021: currently Wednesday at 12:30p Usually 1 or 2 one-on-one or small group meeting during week Contact by email if interested Identify preferred quar ter(s) Number of credits Can take up to 10 credits TCSS 498/499 - CSS elective credits NEXT YEAR - TCSS 498/499 (ANY QUARTER) UNDERGRADUATE READING/RESEARCH IN CSS June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19.
School of Engineering and Technology Daily Feedback Quiz in Canvas – Available After Each Class Extra credit available for completing surveys ON TIME Tuesday surveys: due by ~ Wed @ 11:59p Thursday sur veys: due ~ Mon @ 11:59p June 3, 2021 TCSS422: Computer Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. ONLINE DAILY FEEDBACK SURVEY June 3, 2021 TCSS422: Computer Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19.
School of Engineering and Technology Please classify your perspective on material covered in today’s class (42 respondents): 1-mostly review, 5-equal new/review, 10-mostly new Average – 6.37 ( - previous 6.02) Please rate the pace of today’s class: 1-slow, 5-just right, 10-fast Average – 5.46 ( - previous 5.52) June 3, 2021 TCSS422: Computer Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. MATERIAL / PACE June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. FEEDBACK
School of Engineering and Technology
Assignment 3 provides an introduction to kernel
programming by demonstrating how to create a
Linux Kernel Module
Kernel modules are commonly used to write device
drivers and can access protected operating system data
structures
For example: Linux task_struct process data structure
Assignment 3 is scored in the Quizzes / Activities /
Tutorials category
Lowest two grades in this category are dropped
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. ASSIGNMENT 3: INTRODUCTION TO LINUX KERNEL MODULES
Questions from 6/
Tutorial 2 – Pthread, locks, conditions tutorial – June 4
Assignment 3: (Tutorial) Introduction to Linux Kernel Modules
Final exam – alternate format
Quiz 4 – Page Tables
Chapter 20: Paging: Smaller Tables
Example Question
Chapter 21/22: Beyond Physical Memory
Swapping Mechanisms, Swapping Policies
Practice Questions for “Final” Quiz
5:45 pm – Life After TCSS 422: CSS Career Panel
w/ Soft Eng from UWT CSS Jugal and Navid (eBay and T-Mobile) June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. OBJECTIVES – 6/
School of Engineering and Technology Final Exam category will have two assignments Thursday June 10 from 3:40 to 5:40 pm Final Quiz (50 points) SHORT: fewer than half the number of questions as the midterm 1-hour Focus on new content - since the midterm Tutorial: Linux File Systems and Disk I/O Available for 1-week ~June 5th^ to June 11th 50 points Presents new material in a hands-on, interactive format Complete activity and answer questions Individual work June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. ALTERNATE FINAL EXAM
Questions from 6/
Tutorial 2 – Pthread, locks, conditions tutorial – June 4
Assignment 3: (Tutorial) Introduction to Linux Kernel Modules
Final exam – alternate format
Quiz 4 – Page Tables
Chapter 20: Paging: Smaller Tables
Example Question
Chapter 21/22: Beyond Physical Memory
Swapping Mechanisms, Swapping Policies
Practice Questions for “Final” Quiz
5:45 pm – Life After TCSS 422: CSS Career Panel
w/ Soft Eng from UWT CSS Jugal and Navid (eBay and T-Mobile) June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. OBJECTIVES – 6/
School of Engineering and Technology Consider a 16 MB computer which indexes memory using 4KB pages (#1) For a single level page table, how many pages are required to index memory? (#2) How many bits are required for the VPN? (#3) Assuming each page table entr y (PTE) can index any byte on a 4KB page, how many of fset bits are required? (#4) Assuming there are 8 status bits, how many bytes are required for each page table entry? June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. MULTI-LEVEL PAGE TABLE EXAMPLE (#5) How many bytes (or KB) are required for a single level page table? Let’s assume a simple HelloWorld.c program. HelloWorld.c requires virtual address translation for 4 pages: 1 – code page 1 – stack page 1 – heap page 1 – data segment page (#6) Assuming a two-level page table scheme, how many bits are required for the Page Director y Index (PDI)? (#7) How many bits are required for the Page Table Index (PTI)? June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. MULTI LEVEL PAGE TABLE EXAMPLE - 2
School of Engineering and Technology Assume each page directory entry (PDE) and page table entr y (PTE) requires 3 bytes: 6 bits for the Page Directory Index (PDI) 6 bits for the Page Table Index (PTI) 8 status bits (#8) How much total memory is required to index the HelloWorld.c program using a two-level page table when we only need to translate 4 total pages? HINT: we need to allocate one Page Directory and one Page Table… HINT: how many entries are in the PD and PT June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. MULTI LEVEL PAGE TABLE EXAMPLE - 3 (#9) Using a single page directory entry (PDE) pointing to a single page table (PT), if all of the slots of the page table (PT) are in use, what is the total amount of memor y a two-level page table scheme can address? (#10) And finally, for this example, as a percentage (%), how much memory does the 2-level page table scheme consume compared to the 1-level scheme? HINT: two-level memory use / one-level memor y use June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. MULTI LEVEL PAGE TABLE EXAMPLE - 4
School of Engineering and Technology
CHAPTER 21/22:
BEYOND PHYSICAL
MEMORY
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19.
Disks (HDD, SSD) provide another level of storage in the
memory hierarchy
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19.
MEMORY HIERARCHY
School of Engineering and Technology
Provide the illusion of an address space larger than
physical RAM
For a single process
Convenience
Ease of use
For multiple processes
Large virtual memory space supports running
many concurrent processes...
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. MOTIVATION FOR EXPANDING THE ADDRESS SPACE June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. LATENCY TIMES Design considerations:
SSDs 4x the time of DRAM
HDDs 80x the time of DRAM
Latency numbers ever y programmer should know Fr o m : htt ps://gist.g ithub.co m/jboner/28 41 83 2# file-latency -t xt
School of Engineering and Technology The size of the swap space can be seen using the Linux free command: “free –h” With sufficient disk space, a common allocation is to create Swap space greater than or equal to physical RAM June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. SWAP SPACE - 2 Swap space lives on a separate logical volume in Ubuntu Linux that is managed separately from the root file system Check logical volumes with “sudo lvdisplay” command: See also “lvm lvs” command June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. SWAP SPACE - 3
School of Engineering and Technology
Memory pages are:
Stored in memory
Swapped to disk
Present bit
In the page table entry (PTE) indicates if page is present
Page fault
Memory page is accessed, but has been swapped to disk
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. PAGE LOCATION
OS steps in to handle the page fault
Loading page from disk requires a free memory page
Page-Fault Algorithm
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. PAGE FAULT
School of Engineering and Technology
REPLACEMENT
POLICIES
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. 7 Replacement policies apply to “any” cache Goal is to minimize the number of misses Average memory access time (AMAT) can be estimated: Consider TM = 100 ns, TD = 10ms Consider Phit = .9 (90%), Pmiss =. Consider Phit = .999 (99.9%), Pmiss =. June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19.
CACHE MANAGEMENT
𝐴𝑀𝐴𝑇 = 𝑃ு௧ ∗ 𝑇ெ + (𝑃ெ௦௦ ∗ 𝑇) Argument Meaning 𝑇ெ The cost of accessing memory (time) 𝑇 The cost of accessing disk (time) 𝑃ு௧ The probability of finding the data item in the cache(a hit) 𝑃ெ௦௦ The probability of not finding the data in the cache(a miss)
School of Engineering and Technology What if: We could predict the future (… with a magical oracle) All future page accesses are known Always replace the page in the cache used farthest in the future Used for a comparison Provides a “best case” replacement policy Consider a 3-element empty cache with the following page accesses: 0 1 2 0 1 3 0 3 1 2 1 June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. OPTIMAL REPLACEMENT POLICY
What is the hit/miss ratio?
6 hits
Queue based
Always replace the oldest element at the back of cache
Simple to implement
Doesn’t consider importance… just arrival ordering
Consider a 3-element empty cache with the following
page accesses:
0 1 2 0 1 3 0 3 1 2 1
What is the hit/miss ratio?
How is FIFO different than LRU?
June 3, 2021 TCSS422: Operating Systems [Spring 2021] School of Engineering and Technology, University of Washington - Tacoma L19. FIFO REPLACEMENT
4 hits
LRU incorporates history
