likely() and unlikely()

[Leena M.]

Hi All,

What do likely() and unlikely()  mean ?


I see that it says :

linux-2.6.30.2\linux-2.6.30.2\include\linux\compiler.h"

/*
 * Using __builtin_constant_p(x) to ignore cases where the return
 * value is always the same.  This idea is taken from a similar patch
 * written by Daniel Walker.
 */
# ifndef likely
#  define likely(x)    (__builtin_constant_p(x) ? !!(x) :
__branch_check__(x, 1))
# endif
# ifndef unlikely
#  define unlikely(x)    (__builtin_constant_p(x) ? !!(x) :
__branch_check__(x, 0))
# endif

but can't easliy recognize what is actually intended when likely() and
unlikely() is used ??

for instance :
here
if (likely((atomic_read(&files->count) == 1)))


Regards,
Leena //