(dvi = slow) (vga = fast), 2d performance with dell 2005fpw lcd

[probablydrew]

I have a dell 2005fpw lcd monitor that runs at a native resolution of 1680x1050@60Hz

I am experiencing bad 2d performance under Kubuntu Linux, I would post a screenshot of it but unfortunately everything appears normal in screenshots. It seems to effect every kind of 2d drawing some degree but the best way I have found to maximize the effect of the problem is to open two windows (browser, file manager, doesn't matter) and drag one window over the other in a circular motion. This causes the contents of the windows to turn white (stop being redrawn) or you get the hall-of-mirrors effect where it looks like you have dozens of windows open. If I do this long enough (10 seconds or so) the mouse cursor will stop and the screen will be frozen while the machine takes 5 seconds or so to catch up.

I have tested two different machines and two different monitors (the 2005fpw and an old crt). Every time I get the same results, connected through dvi is slow, vga is fast.

Things I am fairly sure are not to blame:
1. drivers, I experience this problem with both the "nv" drivers and the "nvidia 1.0-8776" drivers
2. motherboard, memory, processor timing issues, I have tested this with two different machines and got the same results:
(nforce 4 - socket 939, geforce 7800gt pcie)
(nforce 570 - socket am2 - geforce 7950gt pcie)
3. desktop environment, this happens with both kde and gnome apps and desktop environments
4. xorg's ability to redraw that fast (assuming all other things are correct), I have a generic oem computer at work running the same distro, with a common intel integrated gpu and 2d performance is dramatically better even though the hardware is worse
5. monitor's ability to display rapidly redrawing windows, this one is kind of obvious but I wanted to mention that the window redrawing problem is not evident when running windows

I am no expert in this area but if I had to hazard a guess as to what the problem is I would say xorg or something else is not correctly detecting the capabilities of the monitor, or my modeline is bad in some way, though I have played around with it quite a bit.


I have quoted my xorg.conf and monitor specs below, and attached my Xorg.0.log since to quote it would go over the post size limit.

xorg.conf

# /etc/X11/xorg.conf (xorg X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the /etc/X11/xorg.conf manual page.
# (Type "man /etc/X11/xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg

Section "Files"
	FontPath	"/usr/share/X11/fonts/misc"
	FontPath	"/usr/share/X11/fonts/cyrillic"
	FontPath	"/usr/share/X11/fonts/100dpi/:unscaled"
	FontPath	"/usr/share/X11/fonts/75dpi/:unscaled"
	FontPath	"/usr/share/X11/fonts/Type1"
	FontPath	"/usr/share/X11/fonts/100dpi"
	FontPath	"/usr/share/X11/fonts/75dpi"
	FontPath	"/usr/share/fonts/X11/misc"
	# path to defoma fonts
	FontPath	"/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
	Load	"i2c"
	Load	"bitmap"
	Load	"ddc"
	Load	"dri"
	Load	"extmod"
	Load	"freetype"
	Load	"glx"
	Load	"int10"
	Load	"type1"
	Load	"vbe"
EndSection

Section "InputDevice"
	Identifier	"Generic Keyboard"
	Driver		"kbd"
	Option		"CoreKeyboard"
	Option		"XkbRules"	"xorg"
	Option		"XkbModel"	"pc105"
	Option		"XkbLayout"	"us"
	Option		"XkbOptions"	"lv3:ralt_switch"
EndSection

Section "InputDevice"
	Identifier	"Configured Mouse"
	Driver		"mouse"
	Option		"CorePointer"
	Option		"Device"		"/dev/input/mice"
	Option		"Protocol"		"ExplorerPS/2"
	Option		"ZAxisMapping"		"4 5"
	Option		"Emulate3Buttons"	"true"
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "stylus"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "stylus"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "eraser"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "eraser"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "InputDevice"
  Driver        "wacom"
  Identifier    "cursor"
  Option        "Device"        "/dev/wacom"          # Change to 
                                                      # /dev/input/event
                                                      # for USB
  Option        "Type"          "cursor"
  Option        "ForceDevice"   "ISDV4"               # Tablet PC ONLY
EndSection

Section "Monitor"
    Identifier     "DELL 2005FPW"
    Option         "DPMS"
    HorizSync      30-83
    VertRefresh    60
    ModeLine       "1680x1050@60" 119 1680 1728 1760 1840 1050 1053 1059 1080 -hsync +vsync
EndSection

Section "Device"
    Identifier     "Nvidia 7800GT"
    Driver         "nvidia"
    Option         "NoLogo"         "1"
    Option         "IgnoreEDID"     "1"
EndSection

Section "Screen"
    Identifier     "Default Screen"
    Device         "Nvidia 7800GT"
    Monitor        "DELL 2005FPW"
    DefaultDepth    24
    Option         "ExactModeTimingsDVI"     "1"
    SubSection     "Display"
        Depth       1
        Modes      "1680x1050" "1024x768" "800x600" "640x480"
    EndSubSection
    SubSection     "Display"
        Depth       4
        Modes      "1680x1050" "1024x768" "800x600" "640x480"
    EndSubSection
    SubSection     "Display"
        Depth       8
        Modes      "1680x1050" "1024x768" "800x600" "640x480"
    EndSubSection
    SubSection     "Display"
        Depth       15
        Modes      "1680x1050" "1024x768" "800x600" "640x480"
    EndSubSection
    SubSection     "Display"
        Depth       16
        Modes      "1680x1050" "1024x768" "800x600" "640x480"
    EndSubSection
    SubSection     "Display"
        Depth       24
        Modes      "1680x1050" "1024x768" "800x600" "640x480"
    EndSubSection
EndSection

2005fpw lcd monitor specs from dell website

native resolution
1680x1050

horizontal scan range
30-83 kHz

vertical scan range
56-75 Hz	(at native res only use 60Hz)

1680x1050 horiz frequency (kHz)
64.6

1680x1050 vertical frequency (Hz)
59.9

1680x1050 pixel clock
119	(digital)
146.25	(analog)

1680x1050 sync polarity
(horizontal)	-
(vertical)	+

I'm running out of ideas, any insight would be greatly appreciated.