Passing `-l$NIX_BUILD_CORES` improperly limits the overall system load.
For a build machine which is configured to run `$B` builds where each
build gets `total cores / B` cores (`$C`), passing `-l $C` to make will
improperly limit the load to `$C` instead of `$B * $C`.
This effect becomes quite pronounced on machines with 80 cores, with
40 simultaneous builds and a cores limit of 2. On a machine with this
configuration, Nix will run 40 builds and make will limit the overall
system load to approximately 2. A build machine with this many cores
can happily run with a load approaching 80.
A non-solution is to oversubscribe the machine, by picking a larger
`$C`. However, there is no way to divide the number of cores in a way
which fairly subdivides the available cores when `$B` is greater than
1.
There has been exploration of passing a jobserver in to the sandbox,
or sharing a jobserver between all the builds. This is one option, but
relatively complicated and only supports make. Lots of other software
uses its own implementation of `-j` and doesn't support either `-l` or
the Make jobserver.
For the case of an interactive user machine, the user should limit
overall system load using `$B`, `$C`, and optionally systemd's
cpu/network/io limiting features.
Making this change should significantly improve the utilization of our
build farm, and improve the throughput of Hydra.
ninja build progress output is not line-base, it overwrites the same
line over and over again with its progress reporting. nix is line-based
though, so ninja-based builds have their progress hidden. pipe ninja
output through cat to avoid this.
Things changed in the Ninja setup-hook:
- Respect installFlags
- Automatically add checkPhase (can be disabled with dontUseNinjaCheck
in the same way as dontUseNinjaBuild and dontUseNinjaInstall). Tests
are only run when "ninja test" exists.
- Error in build phase when build.ninja is missing. We don’t have a
way to fall back to other build methods, so it’s best to be very
clear when we aren’t able to build with ninja
- Set -l flag to 1 when enableParallelBuilding is disabled
* Add setupHook for meson/ninja build
* libhttpseverywhere: Use meson/ninja setupHooks
* jamomacore: Remove superfluous ninja buildInput
* Remove obsolete ninja buildPhases
These are all handled by ninja's setup hook.
* lean2, xcbuild: fix build with ninja setup hook
Ninja is a runtime dependency here. However, cmake can generate Ninja
build files as well to satisfy the setup hook.
* qtwebengine: fix build with ninja setup hook
