I found one bug, see Phab:D2430. However, even after the patch the
#12419: Scheduling bug with forkOS + MVar -------------------------------------+------------------------------------- Reporter: luisgabriel | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: Runtime System | Version: 8.0.1 Resolution: | Keywords: forkOS; | scheduler Operating System: Linux | Architecture: x86_64 | (amd64) Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2430 Wiki Page: | -------------------------------------+------------------------------------- Comment (by luisgabriel): Replying to [comment:3 simonmar]: threadscope profiles don't look identical. I don't think there is an actual problem, just that the program itself isn't very parallel - if you zoom in, there's lots of time in each thread where no work is being done. The difference in scheduling is due to the way that `forkOS` has to hand- shake with the new thread to get its `ThreadId`. Indeed. This example is not very good. I did not expect the profiles to look identical, but it seemed a bit odd to me having a large number of capabilities in idle. Nevertheless, I'm happy to see you identified a bug in the scheduler. Thank you very much for the quick fix! Feel free to close this ticket when the patch lands. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12419#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler