[GHC] #8279: bad alignment in code gen yields substantial perf issue

[GHC]

#8279: bad alignment in code gen  yields substantial perf issue
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        Reporter:  carter                   |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  highest                  |        Milestone:
       Component:  Compiler                 |          Version:  7.7
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by rwbarton):

 The "align *_entry to 32 bytes" patch helped tak a lot (~10%), but made no
 noticeable difference on average over nofib (lots of random changes
 roughly in the range -3% to 3%).

 I don't really understand how shifting the address of code by 16 bytes can
 have such a drastic effect on performance. I guess it must have to do with
 cache lines, but is using one more cache line really so awful?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8279#comment:4>
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