Class 14
CS 202
11 March 2024

On the board
------------

1. Last time
2. Logistics
3. Midterm review, class overview
4. Your questions

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1. Last time

    --WeensyOS

    --page faults

2. Midterm review, logistics

    --75 minute closed-book exam

        - This means no books, no IDEs, etc.

        - Bring id

    --You can use ONE two-sided sheet of notes; formatting requirements listed
    on Web page. 

3. Midterm review, class overview

    Material

    --Readings (see course Web page, the column called "Reading assignment")

    --Labs

    --Homeworks

    --Lectures

        --Operating systems: what are they?

            --goals, purpose

        -- Processes:
            
            -- process's view of memory and registers

            -- stack frames

            -- OS's view of processes

        -- system calls

        -- Process/OS control transfers

        -- Processes birth: fork()/exec()

        -- Shell 

        -- File descriptors 

        -- Redirection, pipelines

        --threads

        --concurrency

            --hard to deal with; abstractions help us, but not completely
                --critical sections
                --mutexes
                --spinlocks
                --condition variables
                --monitors

	    --lots of things can go wrong: safety problems, liveness
	    problems, etc.

                --> lack of sequential consistency makes the problem worse.

	    --What's the plan for dealing with these problems?

	        --safety problems: build concurrency primitives that get
	        help from hardware (atomic instructions, turning off
	        interrupts, etc.) and move up to higher level abstractions
	        that are easy to program with

	        --liveness problems: most common is deadlock, and we
	        discussed strategies for avoiding it. other problems too:
	        starvation, priority inversion, etc.

	    --lots of trade-offs and design decisions
	        --performance v. complexity

	    --lots of "advice". some is literally advice; some is actually
	    required practice in this class.

        --software safety (Therac-25)

        --scheduling

            --intro: when scheduling happens, which metrics, what costs

            --specific disciplines
            
            --lessons and conclusions

        --virtual memory
            
            intro

            paging

            page tables

            virtual memory on the x86-64

                virtual address: [0000 36bits 12bits]

                --entry in L1...L4 page tables:

                    [40 bits  more bits   bottom 3 bits]

                --protection (user/kernel | read/write |  present/not)

                what's a TLB?

            page faults

                mechanics

                costs

                uses

4. Now questions from you all......