Understanding the likely and unlikely Macros in the Linux Kernel: How They Work and Their Benefits
The Linux kernel’s likely
and unlikely
macros help optimize code execution by hinting to the compiler about the expected outcome of conditional statements. These macros use GCC’s __builtin_expect
function, which influences branch prediction and instruction layout. Here’s a detailed breakdown of how they work and their benefits:
Definition and Functionality
The macros are defined as:
#define likely(x) __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)
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