From b3b64a95b9653963a2868278fd0130858a9eb9f0 Mon Sep 17 00:00:00 2001 From: Sergei Trofimovich Date: Fri, 2 Sep 2016 10:26:43 +0100 Subject: haskell-cabal.eclass: unleash full parallelism of parallel ghc I've explored scalability of 'ghc --make -j' a bit in https://ghc.haskell.org/trac/ghc/ticket/9221 Some takeaways: - never specify -j with N > CPU. garbage collector threads waste kernel time running sched_yield() - GHC allocates A Lot: large nursery decreases GC interruptions. We fix it with '-A256M' - for large nursery enabling work-stealing makes GC finish faster on each collection cycle. We fix it with -qb0 While at it move HCFLAGS setup after parallel defaults. That allows user to override defaults with own HCFLAGS. Signed-off-by: Sergei Trofimovich --- eclass/haskell-cabal.eclass | 20 ++++++++------------ 1 file changed, 8 insertions(+), 12 deletions(-) (limited to 'eclass/haskell-cabal.eclass') diff --git a/eclass/haskell-cabal.eclass b/eclass/haskell-cabal.eclass index c1a13300abb0..94ef7f35ad75 100644 --- a/eclass/haskell-cabal.eclass +++ b/eclass/haskell-cabal.eclass @@ -372,24 +372,20 @@ cabal-configure() { cabalconf+=($(cabal-constraint "ghc")) fi + # parallel on all available cores + if ghc-supports-parallel-make; then + # It should have been just -j$(makeopts_jobs) + # but GHC does not yet have nice defaults: + # https://ghc.haskell.org/trac/ghc/ticket/9221#comment:57 + cabalconf+=(--ghc-options="-j$(makeopts_jobs) +RTS -A256M -qb0 -RTS") + fi + local option for option in ${HCFLAGS} do cabalconf+=(--ghc-option="$option") done - # parallel on all available cores - if ghc-supports-parallel-make; then - local max_jobs=$(makeopts_jobs) - - # limit to very small value, as parallelism - # helps slightly, but makes things severely worse - # when amount of threads is Very Large. - [[ ${max_jobs} -gt 4 ]] && max_jobs=4 - - cabalconf+=(--ghc-option=-j"$max_jobs") - fi - # Building GHCi libs on ppc64 causes "TOC overflow". if use ppc64; then cabalconf+=(--disable-library-for-ghci) -- cgit v1.2.3-65-gdbad