Summary about Computer Systems from A Programmer's Perspective

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 a_k to a_k+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

reference

• CSE351: The Hardware/Software Interface
• Computer Systems: A Programmer's Perspective, 2/E
• Introduction to Caches
• Operating Systems:Principles and Practice