There’s a lot of anecdotal evidence out there about what to do and what not to do. Standard wisdom says that malloc is expensive, for example, and realloc is even worse. But for all of the times I’ve seen people say this, I haven’t seen any concrete numbers.

So, let’s make some.

I intend to keep this post updated as a growing list of functions from glibc, to show how they compare to each other, and how efficient they are.

Method:
Loop a million times running each function once, and analysed using kcachegrind

Results

sprintf (100 bytes, 5 variables)     1,752
pthread_create                       1,115 
fclose                                 575
fopen                                  527
pthread_detach                         405
malloc                                 101
free                                    84
pthread_mutex_lock (always available)   31
pthread_mutex_init                      31
pthread_mutex_unlock                    29
gettimeofday                            12
pthread_mutex_destroy                   10
time                                     8
close                                    7
open                                     7