[Bug 58843] New: [945 lvds downclock] Very slow redraw performance

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=58843

          Priority: medium
            Bug ID: 58843
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [945 lvds downclock] Very slow redraw performance
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: lambchop468 at gmail.com
          Hardware: x86 (IA32)
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

Created attachment 72230
  --> https://bugs.freedesktop.org/attachment.cgi?id=72230&action=edit
Patch to manually specify dotclock

With LVDS downclock enabled, redraw for some applications slows down a lot.

Symptoms:
urxvt: very slow - I can see each character being drawn onto the screen
glxgears: running with vblank_mode=0, glxgears runs at about 22.5 FPS. If the
window is hidden (I do not use a compositing window manager), glxgears runs at
315 fps or so.
youtube: In Firefox, playing a video with Adobe Flash, and drm.debug=0x2, I can
see that lvds upclock does not happen for frame updates of the video - lvds is
downclocked for continuous periods of time on the order of seconds (expected
behavior?)
openbox: window decorations draw slowly

Everything was fine for kernel 3.4.9. I upgraded today to 3.7.1 and all of
these showed up. I highly suspect [1], combined with reclocking LVDS taking too
long. I can do a bisect upon request.

My panel doesn't actually advertise lower refresh rates through EDID, so I
patched my kernel to let me manually specify a dotclock (patch attached).

I am using SNA. The same symptoms occur on UXA.

Software:
xf86-video-intel: 2.20.5
xserver: 1.12.4
libdrm: 2.4.38
mesa: 8.0.4
kernel: 3.7.1

Hardware:
Acer Aspire One (ZG5/AOA150) - Intel 945GSE


[1]
http://git.kernel.org/?p=linux/kernel/git/stable/linux-stable.git;a=commitdiff;h=f047e395ddc9da6c307a10629a237502e627ed85;hp=a7b9761d0a2ded58170ffb4d423ff3d7228103f4

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