portage-ng / portage / sys-kernel / linux-headers / 5.4-r2
emerge -vp

These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.51 s (backtrack: 0/20).

[ebuild     UD ] sys-kernel/linux-headers-5.4-r2::gentoo [6.19::gentoo] USE="-headers-only" 106888 KiB

Total: 1 package (1 downgrade), Size of downloads: 106888 KiB

Wall time
2.498 s vs. 0.003 s for portage-ng