#9221: (super!) linear slowdown of parallel builds on 40 core machine -------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #910, #8224 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by slyfox): I've ran '''synth.bash''' benchmark ('''ghc make -j +RTS -A256M''') on current '''ghc-HEAD''' on the following machines: - 4x2 HT desktop, speedup is '''3.9x''' compared to '''-j1''' case (best at -j8) - 12x2 HT haswell VM, speedup is '''12.7x''' compared to '''-j1''' case (best at -j24) - 8x4 HT Power Power7, speedup is '''8.1x''' compared to '''-j1''' case (best at -j12) Very similar speedup is achieved in multiprocess mode (via Makefile in comment:#65). A few facts: - Multiprocess run is ~10% faster than multithreaded. - Specifying N more than logical CPUs available (say, -j100) in '''ghc make -j<N>''' does not lead to severe performance degradation at least on up to 12 core hardware. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9221#comment:71 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler