Well, somewhere along the line after coming back from a two-month stint with work, Debian testing has had an upgrade that caused all four of my Intel i945 family chipset PCs to burn 100% CPU whenever something changed on the screen. It’s no fun waiting several seconds to alt-tab between windows, so here’s the culprit…

Brice Gordlin wrote on 2007-09-11 some fairly optimistic statements about the state of Xorg’s intel drivers and rendering with EXA acceleration:

Several drivers including Intel and ATI r300 already work great with EXA (no need to use XAA + XAANoOffscreenPixmaps anymore) which means Compiz works very smoothly, even when resizing windows. XAA won’t be removed soon though since lots of things needs to be fixed before that

However it appears that this problem is still ongoing.

More recently, it seems that EXA is now the default rendering mode for my Intel chipsets but I had to use the above mentioned fix (revert back to XAA) that apparently wasn’t meant to be necessary any more.

Then I discovered this Ubuntu bug thread where I found there are some options you can set with EXA acceleration which brings performance back up to where XAA was:

xorg.conf:

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Section "Device"
    Identifier      "Intel"
    Driver          "intel"
    BusID           "PCI:0:2:0"
    Option          "AccelMethod" "EXA"
    Option          "ExaNoComposite" "false"
    Option          "MigrationHeuristic" "greedy"
EndSection

Also, a 3D performance tweak can apparently be had by adding this to /etc/environment:

INTEL_BATCH="1"

However, all this breaks accelerated screen rotation, so my potrait display is slow as molasses.

Isn’t Linux fun?