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](http://courses.cs.washington.edu/courses/cse351/)
• [Computer Systems: A Programmer's Perspective, 2/E](http://csapp.cs.cmu.edu/public/code.html)
• [Introduction to Caches](http://www.cs.umd.edu/class/sum2003/cmsc311/Notes/Memory/introCache.html)
• [Operating Systems:Principles and Practice](https://book.douban.com/subject/25984145/)