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

[GHC]

#8224: Excessive system time -- new IO manager problem?
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        Reporter:  rrnewton          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Runtime System    |              Version:  7.7
      Resolution:                    |             Keywords:  IO Manager,
                                     |  System Time
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9221             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Replying to [comment:36 alkar]:
 > > 1. Read all lines from patterns.txt into a set.
 >
 > And the pattern file can be quite large (this is why I'm doing it in a
 single process instead of multiprocessing), so the less penalty I get by
 using `-N` the better.

 Keep in mind that this doesn't necessarily mean that you need a single
 process. With the coming 8.2 release it will be possible to share large
 data structures like your patterns set in a single `mmap`'d shared memory
 block using compact regions. Given the challenges of ensuring good scaling
 with our garbage collector you may want to look into this approach.

 That being said, it would be great if someone (perhaps you!) could look
 into why the system time numbers you report are so high. 30% runtime hit
 on a program which uses only one capability and no parallel GC seems quite
 high.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8224#comment:37>
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