[Bug 75044] New: Repeated mode switching eventually fails

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=75044

          Priority: medium
            Bug ID: 75044
          Assignee: xorg-driver-ati at lists.x.org
           Summary: Repeated mode switching eventually fails
        QA Contact: xorg-team at lists.x.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: dan.doel at gmail.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: Driver/Radeon
           Product: xorg

Created attachment 94145
  --> https://bugs.freedesktop.org/attachment.cgi?id=94145&action=edit
Xorg.0.log from single monitor switching

I recently came into possession of two 4K monitors, and have noticed that
switching modes with them is fairly unreliable. I believe I've put together a
reliable way of triggering the failure now.

My procedure is as follows:

  startx into fluxbox
  xrandr --output DisplayPort-1 --right-of DisplayPort-0
  xrandr --output DisplayPort-1 --mode 1920x1080
  xrandr --output DisplayPort-1 --mode 3840x2160
  ... repeat

The second switch back to 3840x2160 causes both monitors to enter power saving
mode. Subsequently switching to a different virtual terminal and back to the
one running X leaves X dead.

I can also reproduce this with a single monitor. The procedure is the same,
except I turn DisplayPort-1 off, and then switch DisplayPort-0. It requires
more switches to trigger the behavior, but it does eventualy happen.

In all cases, the Xorg log has two lines like the following (this is from the
single monitor case):

  [264287.242] (II) RADEON(0): Allocate new frame buffer 3840x2176 stride 3840
  [264287.248] (EE) RADEON(0): failed to set mode: Invalid argument(II)
RADEON(0): VRAM usage limit set to 1828584K

I assume this means that video memory for the frame buffer has somehow been
exhausted, which explains why it happens faster with two displays, and why it's
more likely to happen with very high resolution displays.

I'll attach dmesg output, Xorg log and xrandr output. Some relevant information
is:

  Kernel 3.12.9
  glamor from git (latest at the time of this post, I believe)
  Mesa 10.2 from git (compiled today)
  xf86-video-ati 7.3.0
  Radeon HD 7870

I found this bug, which sounds like similar behavior:

    https://bugs.freedesktop.org/show_bug.cgi?id=37545

and memory fragmentation is suggested as the problem. However, given that my
problem is triggered by multiple mode switches (I'd say it takes 6-8 in the
single monitor case), perhaps memory is actually being leaked?

If any additional information is desired, I'll try to provide it.

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