c - malloc cpu cycles -

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what cost of malloc(), in terms of cpu cycles? (vista/os, latest version of gcc, highest optimization level,...)

basically, i'm implementing complex dag structure (similar linked list) composed of 16b (less common) , 20b nodes (more common).

occasionally, have remove nodes , add some. but, rather using malloc() , free(), can move unneeded nodes end of data structure, , update fields algorithm continues. if free node available, update fields; if not, i'll have allocate new one.

the problem is, might have 1 free node available while having input, example, 20 nodes worth of data. means:

  • i check available free node
  • the check succeed, , free node updated
  • i check available node 19 more times
  • all checks fail, , malloc() called each time

question: worth it? should malloc() , free() usual, or worth keep free nodes available @ end of list, , keep checking if fail , lead malloc() anyway?

more concretely,

what cpu cost of malloc()??

does matter costs? really?

the true answer "it depends".

it depends on loads of things

  • what else os doing @ time
  • how fragmented memory has become
  • speed of memory , processor on client pc
  • etc

if code massively performance critical, them time everything can , work out best pattern usage case.

if isn't performance critical bit of code, whatever clearest , simplest implement , maintain.

"we should forget small efficiencies, 97% of time: premature optimization root of evil", donald knuth


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