[GHC] #12181: Multi-threaded code on ARM64 GHC runtime doesn't use all available cores

[GHC]

#12181: Multi-threaded code on ARM64 GHC runtime doesn't use all available cores
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        Reporter:  varosi                   |                Owner:
            Type:  bug                      |               Status:  new
        Priority:  normal                   |            Milestone:
       Component:  Runtime System           |              Version:  7.10.3
      Resolution:                           |             Keywords:
Operating System:  Unknown/Multiple         |         Architecture:  arm
 Type of failure:  Runtime performance bug  |            Test Case:
      Blocked By:                           |             Blocking:
 Related Tickets:                           |  Differential Rev(s):
       Wiki Page:                           |
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Comment (by varosi):

 The problem seems to be more deep. Currently we run a program written in C
 for profiling of matrix multiplication and it runs on all cores. When we
 run Haskell program with "+RTS -N8" (fix for number of cores) it runs 8 OS
 threads but they are taking just half of available cores and program runs
 much slower than running it with "+RTS -N4".

 This is the program for reference:
 https://bitbucket.org/varosi/cgraytrace/overview

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12181#comment:3>
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