[GHC] #16034: Quadratic GC slowdown using RTS debug

[GHC]

#16034: Quadratic GC slowdown using RTS debug
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        Reporter:  remyo             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by osa1):

 I don't think this is a bug. As you already found out we do `countBlock()`
 a lot
 in debug runtime for sanity checking (`perf` shows that your example
 spends 72%
 of the time in `countBlocks()`), which traverses linked lists of blocks.
 This
 takes more time as residency increases.

 Out of curiosity, why do you want debug runtime to be faster? Debug
 runtime is
 supposed to make debugging easier, and for that we do lots of sanity
 checking.
 It'd be strange to optimise debug runtime for runtime performance instead
 of ease of
 debugging.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16034#comment:2>
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