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.
Stdenv on aarch64-darwin pulls in (bootstrap-stage4) objc4, unlike
x86_64. However derivations that otherwise depend on objc4 would use a
a different objc4 derivation on top of the final stdenv.
Because this library defines an LLVM module, having multiple instances
of it in the import path will interfere with builds.
The options GCC_PLUGIN_RANDSTRUCT{,_PERFORMANCE} have been renamed to
`RANDSTRUCT_*` in 595b893e2087de306d0781795fb8ec47873596a6 since CLang
is about to support this as well and thus the options had to be
generalized.
Also, the file that is used to generate the seed has changed, only the
reference to the file in the patch was changed on adding Linux 5.19[1]
[1] b4d0cb4497
