#8900: unordered-containers 16% slower in HEAD vs 7.6.3 --------------------------------------------+------------------------------ Reporter: tibbe | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: | Keywords: Operating System: MacOS X | Architecture: x86_64 Type of failure: Runtime performance bug | (amd64) Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by simonmar): So we have {{{ MUT time 0.24s ( 0.24s elapsed) GC time 0.13s ( 0.17s elapsed) vs MUT time 0.25s ( 0.25s elapsed) GC time 0.18s ( 0.23s elapsed) }}} ie. almost all the difference is in GC. And: {{{ 141,978,520 bytes copied during GC 99 MB total memory in use (0 MB lost due to fragmentation) vs 231,158,688 bytes copied during GC 144 MB total memory in use (0 MB lost due to fragmentation) }}} And {{{ Gen 1 8 colls, 0 par 0.07s 0.10s 0.0127s 0.0479s vs Gen 1 13 colls, 0 par 0.12s 0.16s 0.0127s 0.0468s }}} My guess, based on seeing things like this before, is that the benchmark is very sensitive to when exactly major GC strikes - perhaps it has a spike in memory usage at some point. You ought to be able to test this hypothesis by tweaking the GC options. Try with a very large heap size (-A2G). There's a very small change in the MUT time, which is probably accounted for by extra cache misses caused by the extra GC activity. So I suspect this is nothing to worry about. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8900#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler