[GHC] #8224: Excessive system time -- new IO manager problem?

[GHC]

#8224: Excessive system time -- new IO manager problem?
-------------------------------------+-------------------------------------
        Reporter:  rrnewton          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  high              |        Milestone:  7.8.1
       Component:  Runtime System    |          Version:  7.7
      Resolution:                    |         Keywords:  IO Manager,
Operating System:  Linux             |  System Time
 Type of failure:  Runtime           |     Architecture:  x86_64 (amd64)
  performance bug                    |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by AndreasVoellmy):

 I also see the 200ms system time for excessive_system.hs when I run it
 with -N32 (and compiled with recent HEAD). Below is the first few entries
 after running perf record; it looks like it may be GC related. I don't see
 any IO manager related entries in the list.

 {{{
 39.02%  excessive_syste  excessive_system    [.] gcWorkerThread
  15.53%  excessive_syste  [kernel.kallsyms]   [k] __ticket_spin_lock
   6.10%  excessive_syste  [kernel.kallsyms]   [k]
 default_send_IPI_mask_sequence_phys
   5.88%  excessive_syste  excessive_system    [.] allocBlock_sync
   3.95%  excessive_syste  [kernel.kallsyms]   [k] update_sd_lb_stats
   2.76%  excessive_syste  excessive_system    [.] steal_todo_block
   2.18%  excessive_syste  [kernel.kallsyms]   [k] native_write_msr_safe
   1.65%  excessive_syste  libc-2.15.so        [.] 0x7e21f
   1.52%  excessive_syste  excessive_system    [.] evacuate
   0.75%  excessive_syste  [kernel.kallsyms]   [k] dequeue_task_fair
   0.74%  excessive_syste  [kernel.kallsyms]   [k] do_mmap_pgoff
   0.67%  excessive_syste  libc-2.15.so        [.] __clone
   0.67%  excessive_syste  [kernel.kallsyms]   [k] memset
   0.66%  excessive_syste  [kernel.kallsyms]   [k] dequeue_entity
   0.66%  excessive_syste  [kernel.kallsyms]   [k] release_pages
   0.62%  excessive_syste  [kernel.kallsyms]   [k] find_next_bit
   0.58%  excessive_syste  excessive_system    [.] scavenge_until_all_done
   0.56%  excessive_syste  [kernel.kallsyms]   [k] __schedule
   0.54%  excessive_syste  [kernel.kallsyms]   [k] hrtimer_interrupt
  }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8224#comment:2>
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