[GHC] #9221: (super!) linear slowdown of parallel builds on 40 core machine

[GHC]

#9221: (super!) linear slowdown of parallel builds on 40 core machine
-------------------------------------+-------------------------------------
        Reporter:  carter            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  high              |               Milestone:  8.0.1
       Component:  Compiler          |                 Version:  7.8.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #910, #8224       |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by slyfox):

 Didin't try to inspect thunks for TSOs yet. Another datapoint:

 Built whole GHC with ```SRC_HC_OPTS += -feager-blackholing``` and ran on
 the same source from comment 28  with ```-j${i} +RTS -A128M >/dev/null```.

 The best wall-clock (real) result is achieved on -j8 (for box with 8
 logical cores!)

 {{{
 $ for i in `seq 1 40`; do echo "running $i"; time ./mk.bash -j${i} +RTS
 -A128M >/dev/null; done


 running 1

 real    0m45.510s
 user    0m41.844s
 sys     0m2.699s
 running 2

 real    0m26.609s
 user    0m42.121s
 sys     0m4.227s
 running 3

 real    0m20.976s
 user    0m47.452s
 sys     0m5.892s
 running 4

 real    0m18.391s
 user    0m48.771s
 sys     0m7.716s
 running 5

 real    0m16.504s
 user    0m53.015s
 sys     0m9.339s
 running 6

 real    0m16.108s
 user    0m59.391s
 sys     0m12.256s
 running 7

 real    0m15.845s
 user    1m3.952s
 sys     0m15.632s
 running 8

 real    0m15.163s
 user    1m9.096s
 sys     0m14.940s
 running 9

 real    0m15.693s
 user    1m11.332s
 sys     0m17.059s
 running 10

 real    0m16.155s
 user    1m13.646s
 sys     0m18.863s
 running 11

 real    0m16.595s
 user    1m16.520s
 sys     0m19.622s
 running 12

 real    0m19.407s
 user    1m18.191s
 sys     0m22.702s
 running 13

 real    0m17.047s
 user    1m18.216s
 sys     0m22.033s
 running 14

 real    0m17.668s
 user    1m19.592s
 sys     0m24.237s
 running 15

 real    0m18.087s
 user    1m21.217s
 sys     0m26.945s
 running 16

 real    0m18.304s
 user    1m21.447s
 sys     0m28.425s
 running 17

 real    0m18.912s
 user    1m23.788s
 sys     0m29.615s
 running 18

 real    0m19.715s
 user    1m24.838s
 sys     0m32.569s
 running 19

 real    0m20.534s
 user    1m25.534s
 sys     0m31.648s
 running 20

 real    0m21.440s
 user    1m27.836s
 sys     0m42.114s

 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9221#comment:41>
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