Performance tips

TIPS

• Remember the 80/20 rule
  • 80% of a program spends its time in 20% of the code
• Prefer x += y, to x = x + y
• Use pre-incrementation (++i), instead of post-incrementation (i++)
  • This typically applies to any object that has a custom incrementor/decrementor instead of a native type.
• Pre-allocatation of memory will help memory fragmentation
• Don't use dynamic_cast, its a run-time cast operator
• Avoid using printf (printf, sprintf, strftime) functions where alternatives are possible
• Evaluate once, use many times
• In loops if a value doesn't change, evaluate it outside the loop ( don't trust the compiler to optimise )
• Use Just-In-Time (lazy) evaluation where appropriate
  • Don't evaluate something if it will won't be used
  • i.e. evaluate just before using
• Use Object Caching to pre-allocate memory and objects
  • i.e. by overriding new and delete operators
  • Helps not only in performance but also memory fragementation
  • Helps greatly in a system with various different sizes of objects
• Use reference-counting and smart-pointers to avoid excessive memory allocation
• Initialise objects instead of assignement
  • Don't use 'int a; a = 2;'
  • Use 'int a = 2;'
• MEB Specific
  • There are several system calls made every time round each MEB main loop.
  • The MEB is single threaded, hence end->end time is just as important as time of individual components
• System calls
  • system() calls are really expensive. If called frequently look into alternatives
  • sigprocmask is really bad on Linux/gcc, similarly gettimeofday is very expensive as well
  • iostat again is really expensive on Linux/gcc
  • Look into alternatives into all system calls.
• Pcap Issues
  • Standard implementations usually incur a high overhead due to multiple copies of the data
  • Look into alternatives, e.g. PF-RING, etc