#9221: (super!) linear slowdown of parallel builds on 40 core machine -------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: Compile- | Blocked By: time performance bug | Related Tickets: #910 Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by simonmar): We probably want to be running with larger heap sizes when there are lots of cores, to counteract the synchronization overhead of stop-the-world GC across many cores. e.g. `+RTS -A32m` at least. Check whether your machines really have N cores, or if N/2 of those are hyperthreaded cores. I don't recommend including hyperthreaded cores in the -N value you give to GHC, it's better to leave them free to soak up any extra load while letting the GC synchronize properly. @carter, when you said "100% of ghc's cpu time was spent on user-space lock contention when I did the -j40 invocation.", how did you discover that? Which lock in particular? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9221#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler