Operating Systems (CS 161) – Spring 2022

Module Topic: Ethical Tradeoffs in Operating Systems Design: A Look at Cost-Benefit Analysis
Module Author: Sophie Gibert

Course Level: Upper Level Undergraduate
AY: 2020-2021

Course Description: “This course focuses on the design and implementation of modern operating systems. The course discusses threads, processes, virtual memory, schedulers, and the other fundamental primitives that an OS uses to represent active computations. An exploration of the system call interface explains how applications interact with hardware and other programs which are concurrently executing. Case studies of popular file systems reveal how an OS makes IO efficient and robust in the midst of crashes and unexpected reboots. Students also learn how virtualization allows a physical machine to partition its resources across multiple virtual machines. Class topics are reinforced through a series of intensive programming assignments which use a real operating system.” (Course description) 

Semesters Taught: Spring 2019, Spring 2020, Spring 2021, Spring 2022

Tags

• Operating systems [CS]
• Virtualization [CS]
• Cost-benefit analysis [Phil]
• Tradeoffs [Phil]
• Time discounting [Phil]
• Social discount rate [Phil]
• Marketed and non-marketed goods [Phil]
• Incommensurability [Phil]
• Monetization [Phil]
• Aggregation [Phil]
• Distribution [Phil]

Module Overview

In designing operating systems, engineers must often make tradeoffs—for example, between speed and safety, or features and robustness. A common method for making such tradeoffs is cost-benefit analysis (CBA), a normative framework according to which one should do whatever maximizes the overall ratio of benefits to costs. This module acquaints students with CBA and has them apply key parts of CBA to a scenario in operating systems design. It also introduces students to important ethical objections to CBA and helps them identify situations in which CBA is a problematic way of resolving tradeoffs.

    Connection to Course Material

Students in this course learn about operating systems design. CBA is commonly used to resolve the tradeoffs that inevitably arise in operating systems design. It is therefore worth examining CBA in more detail and considering the ethical issues it raises.

Goals

Module Goals

By the end of the module, students will be able to:

1. Describe the steps of CBA and say how it can be used to resolve tradeoffs.
2. Perform several key steps of CBA on a scenario in operating systems design.
3. Explain and evaluate some prominent ethical objections to CBA and say how they are relevant to operating systems.
4. Identify situations in which CBA is a problematic way of resolving tradeoffs.

    Key Philosophical Questions

1. What is CBA, and how is it used in operating systems design?
2. What are some of the most prominent ethical objections to CBA, and at which steps of CBA do they arise?
3. In what situations is CBA a problematic way of resolving tradeoffs?

Materials

    Key Philosophical Concepts

    Assigned Readings

• Boardman et al., “The Basic Steps of CBA: Coquihalla Highway Example,” in Chapter 1 of Cost-Benefit Analysis: Concepts and Practice, 3rd Edition (1996). Select circle icon with letter ‘i’ to read the marginalia for this paragraph
• Hansson, Sven Ove, “Cost-Benefit Analysis: Philosophical Issues,” in The New Palgrave Dictionary of Economics (2010).

Implementation

Class Agenda

1. Professor introduces technical material regarding virtualization and motivates the topic by presenting a real-life case of computer scientists using CBA to resolve a tradeoff (10 minutes)
2. Introduction and preparation for small-group discussion (5 minutes)
3. Activity in small groups: Scaffolded application of CBA to a scenario in operating systems design, aided by a worksheet, pausing at multiple points for class-wide discussion (50 minutes)
4. Class-wide summative discussion of CBA as a method for resolving tradeoffs in operating systems design; concluding remarks (10 minutes)

    Sample Class Activity

Students work in small groups to apply CBA to a fictionalized scenario in operating systems design. They are provided with a worksheet that breaks CBA into 7 steps and prompts them to consider two prominent ethical issues along the way. The 7 steps are:

1. Specify the options
2. Identify stakeholders
3. Determine the costs and benefits of each option
4. Identify a common measure of value
5. Discount future costs and benefits
6. Account for uncertainty
7. Recommend

Steps 1 and 2 are not the focus of this module, so students are provided with two plausible options and a list of key stakeholders. Students do not perform steps 5 or 6 during the module, but step 5 is explored in the post-module assignment. The worksheet therefore focuses on steps 3, 4, and 7. During step 4, students discuss the incommensurability objection to CBA. During step 7, students discuss the distribution/aggregation objection

The fictionalized case is designed by the TA in collaboration with the professor and former TAs. In the case, engineers design an operating system called “Sparrow,” which uses virtualization technology. As the system is tested in preparation for its release, two bugs are discovered: one that disproportionately affects users with non-English keyboard setups, and one that disproportionately affects Windows app users. Students consider whether to proceed in launching the system with the bugs or delay the release date (thereby upsetting shareholders) and fix them

    Module Assignment

Before the module, students answer two reading response questions:

• Boardman, Greenberg, Vining, and Weimer introduce the steps of Cost-Benefit Analysis. Which step seems the most difficult to perform, and why?
• Sven Ove Hansson identifies several philosophical and ethical issues with Cost-Benefit Analysis. Which issue seems the most concerning to you, and why?

After the module, students complete an assignment as part of a problem set. The assignment focuses on step 5, discounting future costs and benefits. Students are introduced to the distinction between marketed and non-marketed goods and the reasons in favor of applying time-discounting to marketed goods and money. They are asked to consider the extent to which these reasons also apply to non-marketed goods, such as human wellbeing. They are then asked to examine some of the future costs and benefits that they identified in step 3 of the in-class activity and explain whether they should be discounted or not. Lastly, the assignment touches on the idea of intergenerational justice and the additional ethical problems that arise when future costs and benefits are likely to befall not-yet-existing future people.

Lessons Learned

Students responded very positively to this module. Engagement was high during the activity portion, and class-wide discussions were lively. The vast majority of the students shared or asked a question at some point.

Students reported that they enjoyed learning about CBA and applying it to the operating systems context. They also reported having gained a lot from discussing the worksheet questions with their classmates and hearing other people share responses they hadn’t thought of.

Pedagogical lessons learned:

• Worksheets are highly effective in this setting. They set clear expectations and provide a lot of structure. This is important in classrooms where students are not used to discussing ethics with their peers.
• They also contribute to engagement by giving students something to write on and minimizing their use of electronics. Writing forces students to put their thoughts onto paper, which can reveal gaps in their reasoning and understanding that would go overlooked in a typical conversation.
• Having students introduce themselves to their small groups at the start of class is effective and especially important in lecture-style classrooms where students are not often asked to speak with their peers