60. Link Time Optimization

The DPDK supports compilation with link time optimization turned on. This depends obviously on the ability of the compiler to do “whole program” optimization at link time and is available only for compilers that support that feature. To be more specific, compiler (in addition to performing LTO) have to support creation of ELF objects containing both normal code and internal representation (called fat-lto-objects in gcc and icc). This is required since during build some code is generated by parsing produced ELF objects (pmdinfogen).

The amount of performance gain that one can get from LTO depends on the compiler and the code that is being compiled. However LTO is also useful for additional code analysis done by the compiler. In particular due to interprocedural analysis compiler can produce additional warnings about variables that might be used uninitialized. Some of these warnings might be “false positives” though and you might need to explicitly initialize variable in order to silence the compiler.

Please note that turning LTO on causes considerable extension of build time.

When using make based build, link time optimization can be enabled for the whole DPDK by setting:

CONFIG_ENABLE_LTO=y

in config file.

For the meson based build it can be enabled by setting meson built-in ‘b_lto’ option:

meson build -Db_lto=true