treewide: drop -l$NIX_BUILD_CORES

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.

1 files changed, 1 insertions, 1 deletions

diff --git a/pkgs/os-specific/linux/trace-cmd/default.nix b/pkgs/os-specific/linux/trace-cmd/default.nix
index d27aaa1f137..0aff1bdd789 100644
--- a/pkgs/os-specific/linux/trace-cmd/default.nix
+++ b/pkgs/os-specific/linux/trace-cmd/default.nix
@@ -35,7 +35,7 @@ stdenv.mkDerivation rec {
   # because the Makefile would not print warnings about too old
   # libraries (see "warning:" in the Makefile)
   postBuild = ''
-    make libs doc -j$NIX_BUILD_CORES -l$NIX_BUILD_CORES
+    make libs doc -j$NIX_BUILD_CORES
   '';
 
   installTargets = [