Code-optimization techniques

The degradation from inefficient use of memory is much greater than that from inefficient use of the caches, because the difference in speed between memory and disk is much higher than between cache and memory.

Code-optimization techniques include the following:

• To minimize the code working set of a program, pack frequently executed code together, while separating infrequently used code. In other words, do not put long blocks of error handling code in line and load frequently called modules next to their callers.
• To minimize the data working set, concentrate frequently used data together and avoid unnecessary references to pages. This can be accomplished by using the malloc() subroutine instead of the calloc() subroutine, initializing data structures immediately before they are used and being sure to free and disclaim allocated space when no longer needed.
• To minimize pinned storage, package pinned code in separate load modules. Make sure it is necessary to use pinned code. Certain system structures (such as mbuf pools) are pinned in memory; do not arbitrarily increase them.
• Real-time techniques can be used, such as the plock() subroutine to pin code in memory, and priorities pinned with the setpri() subroutine.