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[Bug 1486997] Re: Copying a large file causes user interface to stop responding


Phill, thank you for taking the time to report this bug and helping to make Ubuntu better. Please execute the following command only once, as it will automatically gather debugging information, in a terminal:
apport-collect 1486997

** Package changed: linux-lts-utopic (Ubuntu) => linux (Ubuntu)

** Changed in: linux (Ubuntu)
   Importance: Undecided => Low

** Changed in: linux (Ubuntu)
       Status: New => Incomplete

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  Copying a large file causes user interface to stop responding

Status in linux package in Ubuntu:

Bug description:
  If you run, for example, `cp file1 file1-copy` with several GB of
  data, give it a minute, then the user interface stops responding and
  the mouse stops moving. There are occasional glimmers of response but
  it's like watching a video one frame at a time. I would expect the
  user interface to continue to work barring the occasional
  interruption. When the copy completes, or if you can interrupt it, the
  user interface works normally again.

  Despite the specific title, which I'll explain next, the command you
  use doesn't matter. Any heavy and prolonged disc activity does it.
  Ironically, running `ubuntu-bug kernel` to report this problem caused
  the mouse and UI to freeze for a few seconds. Scheduled backups also
  cause it.

  So, why the specific title? This has been reported by other user and
  myself before but in more general terms. Those reports are drowned in
  comments by frustrated users clutching at straws to the point where
  it's hard to see where they're going. I thought it might be helpful to
  limit this bug report to a very specific and easily testable example
  so that we don't get side-tracked working around what is probably a
  kernel scheduling issue.

  This is not an isolated or new problem. I've been using ubuntu since
  2008 on several different machines and it's always been a problem.
  Maybe it's a little worse now, maybe not. In any case, there's no
  point bisecting the kernel as it's not a regression.

  The problem also affects the terminal. If you switch to another TTY
  the log-in takes ages, and usually doesn't complete until the heavy
  disk activity has finished. This can be extremely frustrating when you
  don't know which process is making mischief and you want to use a
  terminal to find it and stop it.

  It is possible to alleviate the problem by disabling swap. I did this
  on the hunch that processes were being frozen while memory was paged
  in from the disk. Unfortunately my current workload makes this
  solution impractical. What's odd is that the problem occurs even when
  there's several GB of memory to spare. After re-enabling swap you need
  to wait a little before re-testing to reproduce the problem.

  I've also tried other kernel schedulers. None help.

  I'm a software developer and happy to get my hands dirty, but sadly
  I'm quite unfamiliar with the kernel.

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: linux-image-3.16.0-45-generic 3.16.0-45.60~14.04.1
  ProcVersionSignature: Ubuntu 3.16.0-45.60~14.04.1-generic 3.16.7-ckt14
  Uname: Linux 3.16.0-45-generic x86_64
  ApportVersion: 2.14.1-0ubuntu3.12
  Architecture: amd64
  CurrentDesktop: Unity
  Date: Thu Aug 20 12:21:59 2015
  InstallationDate: Installed on 2015-07-13 (37 days ago)
  InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
  SourcePackage: linux-lts-utopic
  UpgradeStatus: No upgrade log present (probably fresh install)

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