What kernels are built?

So I have my systemm on nix flakes with nixpkgs.url="github:NixOS/nixpkgs/nixos-unstable and the automatic daily updates one thing I’ve found is that while other packages are fetch from the nixos cache the linux kernel is often built from source,even through I’m using the defuault (now 5.10). What are the kernels built on hydra and how do I reduce the amounts of locally compiled packages?

looks like a pretty large rebuild was merged. In general though, the kernelpackages are built pretty quickly.

Kind of suprised there’s not a nixos hydra job for the default linuxPackages though…

I’m pretty sure nixos-unstable isn’t supposed to update until the kernel has been built and cached. This seems odd.

So I have 2 configs,one of which builds an iso installer with a subset of the config files from my main nixos config.
The iso installer does not require a kernel rebuild,despite both having boot.kernelPackages=pkgs.linuxPackages_latest;

So what nixos options could influence the kernel derivation ?

So I’vbe discovered that if I comment boot.crashDump.enable=true; it won’t rebuild the linux kernel anymore.
Options that apply patches to the kernel really should be marked as such.