[GHC] #9105: Profiling binary consumes CPU even when idle on Linux.

[GHC]

#9105: Profiling binary consumes CPU even when idle on Linux.
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       Reporter:  robinp    |             Owner:
           Type:  bug       |            Status:  new
       Priority:  normal    |         Milestone:
      Component:  Compiler  |           Version:  7.8.2
       Keywords:            |  Operating System:  Linux
   Architecture:  x86       |   Type of failure:  None/Unknown
     Difficulty:  Unknown   |         Test Case:
     Blocked By:            |          Blocking:
Related Tickets:            |
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 The program is
   main = forever $ threadDelay 1000000 >> return () .

 Compiled with 32bit GHC 7.6.3 or 7.8.2 on Debian (inside a VM), GHC 7.4.1
 on Ubuntu (not VM).
 The non-profiling binary doesn't consume CPU, the profiling does ~10% (of
 a 2Ghz machine). Running with +RTS -I0, so this is not the idle gc.

 When strace-ing, the profiling one seems to receive a constant flow of
 SIGVTALRM, while the normal receives one burst each second.

 I see I can switch off "master tick interval" with -V0, and then CPU is
 not used, but the consequences of this are not very well documented (apart
 from context switching becoming deterministic).

 Interestingly, if I compile using profiling on Windows (latest haskell-
 platform, 64bit), it doesn't use more CPU than the non-profiling.

 So, the question is, why does this happen on Linux, and if it can be
 avoided somehow.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9105>
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