[Bug 364359] [NEW] xserver 1.6.0 - High %CPU/Power Usage with Intel GM965

[Richard Guo]

Public bug reported:

Binary package hint: xserver-xorg-video-intel

This issue is a regression from Hardy. I did a clean install of Kubuntu
Jaunty RC, using ext4 for partitions. Then I disabled composite effects
via xorg.conf and KDE4 settings. The first thing I noticed was that the
laptop (Lenovo T61 with Intel GM965 card) was *noticeably* warmer than
before, to the point where I can't use it on my lap anymore.

I did some measurements using powertop and top to find the guilty
process.

Top showed the process Xorg taking up 20% of CPU just to redraw the top
output. Nothing was open except the konsole window where the testing was
done. This is in comparison with 1-2% CPU usage on idle for Hardy.

Powertop showed fewer causes for wakeup than before (~100 vs ~180 with
KDE3 on Hardy), but the CPU spent more time in higher P-states (14% vs
1%). This is consistent with the Xorg process usage that top showed.
Absolute power consumption under battery operation. In hardy (sorry, I
don't have the output of powertop on hardy), the power use was 12 W with
wireless on, idle, and the dimmest screen brightness. In Jaunty, I'm
seeing consumption in excess of 15W under the same conditions.

The line "58.5% ( 98.2)       <interrupt> : i915 at pci:0000:00:02.0" made
me think that something was wrong with the latest Intel video drivers.

I have also attached my xorg.conf file, which has very little deviance
from defaults (most notably EXA acceleration). The output of lspci -vv
is also included.

In short, I suspect that this problem is due to Intel 2D causing Xorg to
do a lot of redraws. Text in particular seems to be slow to process
(slow konqueror scrolling).

With some research, I also found that framebuffer compression is
disabled in the 2.6.3 driver due to a bug. That may have caused an
additional spike in power draw.

** Affects: xserver-xorg-video-intel (Ubuntu)
     Importance: Undecided
         Status: New

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xserver 1.6.0 - High %CPU/Power Usage with Intel GM965
https://bugs.launchpad.net/bugs/364359
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