[GHC] #15891: Excessive system time during execution of GHC-built executables on macOS

[GHC]

#15891: Excessive system time during execution of GHC-built executables on macOS
---------------------------------+----------------------------------------
        Reporter:  goldfire      |                Owner:  (none)
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:  8.6.3
       Component:  Compiler      |              Version:  8.6.2
      Resolution:                |             Keywords:
Operating System:  MacOS X       |         Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
---------------------------------+----------------------------------------

Comment (by gridaphobe):

 I'm noticing similar behavior on my macbook.

 System information:
 {{{
 macOS Mojave, 10.14
 Processor: 2.6 GHz Intel Core i7
 Memory: 16 GB 2133 MHz LPDDR3
 SSD main storage, formatted with APFS
 happy 1.19.9
 alex 3.2.4
 gcc is clang-1000.11.45.5, Apple LLVM version 10.0.0, thread model: posix
 bootstrap ghc is 8.4.4
 BuildFlavour = devel2
 }}}

 Just like Richard, the stage1 build is snappy, but things slow down when I
 start using ghc-stage1. I also noticed a sudden jump to 40% system time
 (compared to 10% user time and 50% idle) when I started using ghc-stage1.
 I'm not sure how to sample ghc, but I ran the
 [https://gist.github.com/gridaphobe/dd3df6616720c571548584160912b950
 dtruss command]. I don't really know what to make of the dtruss output,
 but I'm happy to run any other suggested tests.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15891#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler