Poor display performance w/Intel 945GM, cannot enable desktop effects

What happens if you put this in your xorg.conf:

Section "Device"
    ...
    Option "MigrationHeuristic" "greedy"
EndSection

After adding:
  Option "MigrationHeuristic" "greedy"
to xrog.conf, nothing really changed.

Intel-graphics is still software rendered, can't enable compiz.

I'd like to post here the exact reason for the failure. How can I increase verbosity of the appropriate component before I try to enable "desktop effects"? (and where can I grab the logs)

Xorg log shows:
(EE) intel(0): Cannot support DRI with frame buffer width > 2048.

which is caused by this setting in your xorg.conf
Virtual 2560 1024

If you want to use compiz, you will need to reduce the virtual display width to a maximum of 2048.

I'm using a display size of 1280x1024 @ 60 and afaik virtual display is set to same size.
Are there any indications that I'm using "higher than supported" settings?

Whoops! I didn't read all the way through the last response, completely ignore my previous comment.

Thanks for the tip . Indeed, the large size of the virtual desktop was the problem.
I was trying to have dual-monitor setup w/the laptop and a 19" monitor (1290x1024).
At some point the "Display-Preferences" app messed up w/the xorg.conf and I didn't notice that.
It expanded the virtual size of the desktop to 2560x1024 which IS higher than supported.

I guess my lesson is not to expect a larger then 2048 virtual desktop from the 945?
This essentially means no decent dual-monitor support from this laptop... or am I missing something?

udude: Nope, that's it, 2048 is your max, which means my external monitor is limited to 1024 if I want it left-of or right-of the internal screen. I only have an ancient 17" so it doesn't bother me, but I agree it doesn't seem reasonable.

I don't know if there are any plans to change this limitation... I'll dig through the wishlists and if I can't find this request in there, I'll post one. Might be a hardware limit though.

What's interesting is that when I boot WinXP (shhh... I know) I can setup the dual-monitor side-by-side quite nicely. It looks like 945 hw supports this virtual-desktop size. Well, at least in 2D hw-accelerated mode...

Also, looks like I found a bug (not sure if a bug-report already exists):
I created a virtual desktop in which the displays are one on top of the other:
Laptop LCD is 1280x800
External monitor is 1280x1024
virt desktop is 1280x1824, which is within the limits of 2048^2.
This 'kinda' worked. By 'kinda' I mean that both displays work w/compiz, however the background of the secondary monitor does not repaint when dragging windows, and half of the primary display suffers from the same problem.

I tried to create a screen shot but ironically it does not capture the problem... the desktop snapshot looks perfectly fine

Attaching a screenshot anyway, from the primary screen.
It also demonstrates a problem:
Primary screen is 1280x800, but screenshot ends up being 1024x768
(see attached image)

I had problems setting up more than 2048 width for the virtual screen. Even with 3D effects completely disabled, scrolling through a web page or document is a pain...

Does scrolling work OK under windows?
(can't test it, now windows here)

cmavr - I've seen what you're describing. When the virtual desktop is larger than 2048, all video rendering was done in sw (compiz disabled) and yes, usability is a serious pain. Scrolling (and other 2d acceleration) works just fine w/windows.

Looks like there's a fresh thread that discusses this issue:
https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/146859

Looks like the main bug that tracks this issue