[GHC] #16065: Stack squeezing during context switches makes for non-determinism in allocations

18 Dec 2018

      #16065: Stack squeezing during context switches makes for non-determinism in
allocations
-------------------------------------+-------------------------------------
           Reporter:  sgraf          |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:  ⊥
          Component:  Runtime        |           Version:  8.6.3
  System                             |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #4450, #8861
Differential Rev(s):                 |         Wiki Page:
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 As #4450 and #8611 show, stack squeezing in the RTS makes allocation
 numbers between two different runs of the same binary non-deterministic,
 because its effect is depending on when context switches are bound to
 happen.

 A short-term solution might be to deactivate stack squeezing for
 vulnerable benchmarks with `+RTS -Z` like in Phab:D5460, but IMO a more
 elegant solution would be to only deactivate stack squeezing in
 `threadPause` calls that happen due to context switches. Would you agree?

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16065
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