[GHC] #12419: Scheduling bug with forkOS + MVar
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Mon Aug 1 14:34:43 UTC 2016
#12419: Scheduling bug with forkOS + MVar
-------------------------------------+-------------------------------------
Reporter: luisgabriel | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 8.0.2
Component: Runtime System | Version: 8.0.1
Resolution: | Keywords: forkOS;
| scheduler
Operating System: Linux | Architecture: x86_64
| (amd64)
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D2430
Wiki Page: |
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Comment (by luisgabriel):
Replying to [comment:3 simonmar]:
> I found one bug, see Phab:D2430. However, even after the patch the
threadscope profiles don't look identical. I don't think there is an
actual problem, just that the program itself isn't very parallel - if you
zoom in, there's lots of time in each thread where no work is being done.
The difference in scheduling is due to the way that `forkOS` has to hand-
shake with the new thread to get its `ThreadId`.
Indeed. This example is not very good. I did not expect the profiles to
look identical, but it seemed a bit odd to me having a large number of
capabilities in idle.
Nevertheless, I'm happy to see you identified a bug in the scheduler.
Thank you very much for the quick fix! Feel free to close this ticket when
the patch lands.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12419#comment:5>
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