Summary about Computer Systems from A Programmer's Perspective

2017-05-16

ch5 Optimizing Program Performance

  • trade-off between how easy a program is to implement and maintain, and how fast it runs

    • Select an appropriate set of algorithms and data structures
    • make the compiler optimize the code effectively

  • The limitations of optimizing compilers -

    • reducing excessive function calls
    • eliminating unneeded memory references - introduce temp variables to hold intermediate rsults

  • program profiling

  • Amdahl's Law

    • The performance gain depends both on xhow much we improve this part and how large a fraction of the overall time this part originally required

ch6 The Memory Hierarchy

  • Storage Technologies - trade-off between price and performance (access times)

    • Static Random-Access memory(SRAM) - stable - cache memory
    • Dynamic RAM - sensitive to any disturbance - main memory
    • Solid state dist (SSD)
    • rotating disk

  • DRAM and disk access times are much larger than CPU CYCLE TIMES

    • So systems bridge the gaps by organizing memory as a hierarchy of storage devices
    • locality - try to bridge the processor-memory gap
    • temporal locality - locate same data objects multiple time
      • spatial locality - nearby memory location

  • programs with good locality access most of their data from fast cache memories

    • Exploiting SRAM-based cache memories
      • programs that fetch data primarily from cache memories can run much faster than ones that fetch data primarily from memory
    • temporal locality - using a data object as often as possible once it has been read from memory
    • spatial locality - by reading data objects sequentially, with stride 1, in the order they are stored in memory

ch7 Linking - enable separate compilation (just only recompile one source and relink )

  • Linking - concatenates blocks together, and decides on run-time locations for the concatenated blocks

    • symbol resolution step - symbol table in .symtab

      • associate each global symbol (functions and global variables) reference with a unique symbol definition

    • relocation - associate a memory location with each symbol definition, and then make them point to the memory location

      • meger all sections of the same type into a new aggregate section
      • relocate symbol references so that they point to the correct run-time addresses

  • linking with static libraries

    • related functions can be compiled into separate object modules and then packaged in a single static library file; At link time, the linker will copy only the object modules(symbol resolution) that are referenced by the program.

    • advantages

      • need to maintain and update the static libraries periodically
      • At run time, the code of the functions like I/O functions is duplicated in the text segment of each running process

  • dynamic linking with shared libraries

    • a single copy of the .text section of a shared libray in memory can be shared by different running
    • the basic idea is to link the relocation and symbol table info when the executable file is created, and then complete the linking process (code and data ) dynamically when the program is loaded

ch8 Exceptional Control Flow (ECF)

  • control flow (a sequence of control transfer) of the processor

    • control transfer - from the address ak to ak+1

  • Exception - a change in the processor's state (event) triggers an abrupt control tansfer (an exception)

    • an abrupt change in the control flow in response to some change in the processor's state

    • The change in processor's state is known as an event

    • interrupt handling - occurs as a result of events in I/O device

    • traps handling - a procedure-like interface between user programs and the kernel known as a system call
    • fault handling - result from error conditions
    • abort handling

  • process - take turns using the processor

    • an independent logical control flow

    • a private address space

    • concurrent flows - a logical flow whose execution overlaps in time with another

    • The fork function runs the same program (a collection of code and data) in a new child process that is a duplicate of the parent. The execve function loads and runs a new program in the context of the current process. ?

    • signals

    • [TODO]

ch9 Virtual Memory

  • [TODO]

Network programming

  • client-server connections <- slow client

    • full-duplex
    • reliable

  • concurrent Servers

    • based on process
    • based on threads

  • web servers

    • HTTP

  • Concurrent programming if they overlap in time

    • processes
    • I/O multiplexing
    • Threads

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