haskell: tune generic-builder for more parallel build performance

Raise the maximum number of cores used for parallel building from 4 to 16.
Increase the size of the allocation area for GHC's garbage collector from 1 MiB
to 64 MiB.

See https://www.twitch.tv/videos/611899011 for the motivation for this change.

1 files changed, 9 insertions, 11 deletions

diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index ac22f903c9b..49cbe02b71e 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -48,12 +48,8 @@ in
 , isExecutable ? false, isLibrary ? !isExecutable
 , jailbreak ? false
 , license
-# We cannot enable -j<n> parallelism for libraries because GHC is far more
-# likely to generate a non-determistic library ID in that case. Further
-# details are at <https://github.com/peti/ghc-library-id-bug>.
-#
-# Currently disabled for aarch64. See https://ghc.haskell.org/trac/ghc/ticket/15449.
-, enableParallelBuilding ? ((stdenv.lib.versionOlder "7.8" ghc.version && !isLibrary) || stdenv.lib.versionOlder "8.0.1" ghc.version) && !(stdenv.buildPlatform.isAarch64)
+  # aarch64 sometimes crashes for -jn with n>1: https://ghc.haskell.org/trac/ghc/ticket/15449
+, enableParallelBuilding ? !stdenv.buildPlatform.isAarch64
 , maintainers ? []
 , doCoverage ? false
 , doHaddock ? !(ghc.isHaLVM or false)
@@ -82,7 +78,7 @@ in
   # same package in the (recursive) dependencies of the package being
   # built. Will delay failures, if any, to compile time.
   allowInconsistentDependencies ? false
-, maxBuildCores ? 4 # GHC usually suffers beyond -j4. https://ghc.haskell.org/trac/ghc/ticket/9221
+, maxBuildCores ? 16 # more cores usually don't improve performance: https://ghc.haskell.org/trac/ghc/ticket/9221
 , # If set to true, this builds a pre-linked .o file for this Haskell library.
   # This can make it slightly faster to load this library into GHCi, but takes
   # extra disk space and compile time.
@@ -181,6 +177,8 @@ let
     (optionalString enableHsc2hsViaAsm "--hsc2hs-option=--via-asm")
   ];
 
+  parallelBuildingFlags = "-j$NIX_BUILD_CORES" + optionalString stdenv.isLinux " +RTS -A64M -RTS";
+
   crossCabalFlagsString =
     stdenv.lib.optionalString isCross (" " + stdenv.lib.concatStringsSep " " crossCabalFlags);
 
@@ -199,7 +197,7 @@ let
     "--package-db=$packageConfDir"
     (optionalString (enableSharedExecutables && stdenv.isLinux) "--ghc-option=-optl=-Wl,-rpath=$out/lib/${ghc.name}/${pname}-${version}")
     (optionalString (enableSharedExecutables && stdenv.isDarwin) "--ghc-option=-optl=-Wl,-headerpad_max_install_names")
-    (optionalString enableParallelBuilding "--ghc-option=-j$NIX_BUILD_CORES")
+    (optionalString enableParallelBuilding "--ghc-options=${parallelBuildingFlags}")
     (optionalString useCpphs "--with-cpphs=${cpphs}/bin/cpphs --ghc-options=-cpp --ghc-options=-pgmP${cpphs}/bin/cpphs --ghc-options=-optP--cpp")
     (enableFeature (enableDeadCodeElimination && !stdenv.hostPlatform.isAarch32 && !stdenv.hostPlatform.isAarch64 && (versionAtLeast "8.0.1" ghc.version)) "split-objs")
     (enableFeature enableLibraryProfiling "library-profiling")
@@ -227,9 +225,9 @@ let
 
   setupCompileFlags = [
     (optionalString (!coreSetup) "-${nativePackageDbFlag}=$setupPackageConfDir")
-    (optionalString (isGhcjs || isHaLVM || versionOlder "7.8" ghc.version) "-j$NIX_BUILD_CORES")
-    # https://github.com/haskell/cabal/issues/2398
-    (optionalString (versionOlder "7.10" ghc.version && !isHaLVM) "-threaded")
+    (optionalString enableParallelBuilding (parallelBuildingFlags))
+    "-threaded"       # https://github.com/haskell/cabal/issues/2398
+    "-rtsopts"        # allow us to pass RTS flags to the generated Setup executable
   ];
 
   isHaskellPkg = x: x ? isHaskellLibrary;