Re: [GHC] #13497: GHC does not use select()/poll() correctly on non-Linux platforms

31 Mar 2017

      #13497: GHC does not use select()/poll() correctly on non-Linux platforms
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        Reporter:  nh2               |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #8684, #12912     |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nh2):

 Some comments I've found in the code base:

 {{{
     switch (recent_activity) {
     case ACTIVITY_INACTIVE:
         if (force_major) {
             // We are doing a GC because the system has been idle for a
             // timeslice and we need to check for deadlock.  Record the
             // fact that we've done a GC and turn off the timer signal;
             // it will get re-enabled if we run any threads after the GC.
             recent_activity = ACTIVITY_DONE_GC;
 }}}

 {{{
     switch (recent_activity)
     {
     case ACTIVITY_DONE_GC: {
         // ACTIVITY_DONE_GC means we turned off the timer signal to
         // conserve power (see #1623).  Re-enable it here.
 }}}

 So the disabling of the timer signal is a power saving feature.

 I don't understand though why this is only done after a certain time
 (`idleGCDelayTime / tickInterval` many ticks) instead of immediately. Is
 there something we know only after that many ticks? Or is it a performance
 optimisation to do it after that many ticks instead of immediately?

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13497#comment:13
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