Ubuntu is still building for CPUs with the x86-64-v1 feature set. On experimental images built for x86-64-v3 (roughly the feature set of 10 year old CPUs, a bit newer on low-power CPUs) they have observed 60% improvement on some benchmarks (and much less in some others). Some distros have switched to -v3, Ubuntu is still holding out to support older hardware. The author is compiling to the actual feature set of their specific CPU, which is nearly guaranteed to be even more than -v3.
Another thing the article adds is LTO, which in my experience also makes a huge difference: it makes your software a lot faster in certain cases, but also makes build times a lot worse. Spending a bit more time in the build process should be an easy call, but might be harder at the scale of a distro.
I was under the, evidently naive, understanding that there were some shenanigans done in the libc to pick optimal code paths based on the architecture. This would obviously have a startup cost on the first run, but presumably the dynamic linking would work to this advantage by having it in a fast state for most calls?
Not sure where I got that idea, though. :(. Will have to look into that later.
Even if libc does it, other packages wouldn’t. The compiler is what generates code and they generally don’t try to automatically generate for different instruction sets because they don’t know what code is what hotpath and worth optimizing for. You could probably try to build for multiple different CPU features at the top level and do a universal executable like Apple did for their CPU transitions but that’s a lot of expense to pay both in terms of compilation time AND in terms of size.
Another thing the article adds is LTO, which in my experience also makes a huge difference: it makes your software a lot faster in certain cases, but also makes build times a lot worse. Spending a bit more time in the build process should be an easy call, but might be harder at the scale of a distro.