[GHC] #11783: Very large slowdown when using parallel garbage collector

[GHC]

#11783: Very large slowdown when using parallel garbage collector
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           Reporter:  luispedro      |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Runtime        |           Version:  7.10.3
  System                             |
           Keywords:  performance,   |  Operating System:  Unknown/Multiple
  garbage collector                  |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 As part of debugging some performance issues on an application I am
 writing, I concluded that the issue is in the parallel GC implemented in
 the GHC RTS. I extracted the code attached to make a self-contained use-
 case, but in my system the code runs in 16s when using a single thread, in
 18s when using 6 threads but no parallel GC and in over a minute when
 using 6 threads with parallel GC!

 The true slowdown in the full code is actually worse and relevant for the
 application (some steps take >1 hour instead of <1 minute!). Parts of the
 code do take full advantage of parallel processing, this is just one
 simple test case

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11783>
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