Massively reduce the time it takes running the test by building a
proper root disk image and increasing the virtualized core count to
4. This should make it much easier for the tests to pass even on
weaker systems.
With my laptop (AMD Ryzen 7 PRO 2700U, 32GB RAM) as the reference
system, I see the following test run times:
- No change:
25 mins, 49 secs
- Building a root image:
4 mins, 44 secs
- Building a root image and bumping the core count:
3 mins, 6 secs
The times include the time it takes to build the image (~40 secs).
Make sure the all derivations referenced by the test script are
available on the nodes. Accessing these derivations works just fine
without this change when using 9p to mount the host's store, but when
an image is built (virtualisation.buildRootImage), the dependencies
need to be copied to the image. We don't want to copy the script
itself, though, since that would trigger unnecessary image rebuilds.
Add writeStringReferencesToFile, a builder which extracts a string's
references to derivations and paths and writes them to a text file,
removing the input string itself from the dependency graph. This is
useful when you want to make a derivation depend on the string's
references, but not its content (to avoid unnecessary rebuilds, for
example).
pathsInNixDB isn't a very accurate name when a Nix store image is
built (virtualisation.useNixStoreImage); rename it to additionalPaths,
which should be general enough to cover both cases.
Add the `useNixStoreImage` option, allowing a disk image with the
necessary contents from the Nix store to be built using
make-disk-image.nix. The image will be mounted at `/nix/store` and
acts as a drop-in replacement for the usual 9p mounting of the host's
Nix store.
This removes the performance penalty of 9p, drastically improving
execution speed of applications which do lots of reads from the Nix
store. The caveats are increased disk space usage and image build
time.
Add a copyChannel argument which controls whether the current source
tree will be made available as a nix channel in the image or
not. Previously, it always was. Making it available is useful for
interactive use of nix utils, but changes the hash of the image when
the sources are updated.
