#12419: Scheduling bug with forkOS + MVar -----------------------------------------+--------------------------------- Reporter: luisgabriel | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 8.0.1 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): | Wiki Page: -----------------------------------------+--------------------------------- I have noticed a weird scheduling behavior when performing some experiments with the '''fasta''' benchmark [1] from The Computer Language Benchmarks Game. When I switch `forkIO` by `forkOS` the scheduler stops to assign work for some capabilities, and they stay idle for the whole execution of the program. ThreadScope view using forkIO: https://s31.postimg.org/r3mclspe3/fork_IO_N8_ghc8.png ThreadScope view using forkOS: https://s31.postimg.org/p9n265fff/fork_OS_N8_ghc8.png I was able to reproduce this behavior in both '''GHC 7.10.2''' and '''GHC 8.0.2'''. I was also able to reproduce it on two different machines running Ubuntu Server 14.04.3 LTS (kernel 3.19.0-25): - 2x10-core Intel Xeon E5-2660 v2 processors (Ivy Bridge), 2.20 GHz, with 256GB of DDR 1600MHz - 4-core Intel i7-3770 (IvyBridge) with 8 GB of DDR 1600MHz Source code + .eventlog files: https://dl.dropboxusercontent.com/u/5798150 /fasta-bug.zip [1] http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=ghc&id=7 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12419 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler