[GHC] #9890: RTS -qa option is helpful but under-documented

[GHC]

#9890: RTS -qa option is helpful but under-documented
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       Reporter:  adamgundry         |                   Owner:
           Type:  task               |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Runtime System     |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  Documentation bug
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 The entire documentation for the RTS `-qa` option is

     Use the OS's affinity facilities to try to pin OS threads to CPU
 cores. This is an experimental feature, and may or may not be useful.
 Please let us know whether it helps for you!

 It does help for us: enabling it on a multithreaded, moderately GC-heavy
 web server led to a sizeable improvement (~20%) in throughput benchmarks.
 However, it would be nice if the GHC documentation was a little more
 descriptive about what exactly this option does and how experimental it is
 now considered! (Relatedly, perhaps it would be worth adding a single
 index of RTS options in the user's guide, much like the flag reference for
 GHC itself.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9890>
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