commit: b3b64a95b9653963a2868278fd0130858a9eb9f0
Author: Sergei Trofimovich <slyfox <AT> gentoo <DOT> org>
AuthorDate: Fri Sep 2 09:26:43 2016 +0000
Commit: Sergei Trofimovich <slyfox <AT> gentoo <DOT> org>
CommitDate: Fri Sep 2 09:29:51 2016 +0000
URL: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=b3b64a95
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<N> 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 <slyfox <AT> gentoo.org>
eclass/haskell-cabal.eclass | 20 ++++++++------------
1 file changed, 8 insertions(+), 12 deletions(-)
diff --git a/eclass/haskell-cabal.eclass b/eclass/haskell-cabal.eclass
index c1a1330..94ef7f3 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)
