freebsd stable - Jan 2008 - Low CPU Freq responsible for xterm pixel corruption on RELENG_7

Some weeks ago, I posted on the x11@ list of a problem of pixel corruption
I am seeing in xterm windows.  An example of the problem can still be
seen here:
	http://opal.com/jr/xterm-corruption.gif

Quick summary: Wide xterm windows (wider than 158 columns, 1440 pixels)
have the problem shown, but only when at least that many columns are on
the screen.  That is, moving a wide window so that it is partially off
the screen causes the corruption to cease when less than 158 columns
are displayed.

Further investigation has unearthed that this problem happens only when
the CPU frequency is set to low levels, which was happening because of
powerd.  When the CPU frequency is set low, these pixel corruptions happen.
When the CPU freq is raised they do not: everything is normal.

Disabling powerd and manually adjusting the CPU frequency gives these results:

# sysctl dev.cpu.0.freq_levels
dev.cpu.0.freq_levels: 3176/-1 2779/-1 2382/-1 1985/-1 1588/-1 1191/-1 794/-1
397/-1

CPU freq from 3176 to 1191 causes no problems.
CPU freq at 794 or 397 causes pixel corruptions.

This problem did not happen on RELENG_6.

	-jr
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On Sun, Jan 27, 2008 at 08:54:00PM -0500, J.R. Oldroyd
wrote:
> Some weeks ago, I posted on the x11@ list of a problem of pixel corruption
> I am seeing in xterm windows.  An example of the problem can still be
> seen here:
> 	http://opal.com/jr/xterm-corruption.gif
> Quick summary: Wide xterm windows (wider than 158 columns, 1440 pixels)
> have the problem shown, but only when at least that many columns are on
> the screen.  That is, moving a wide window so that it is partially off
> the screen causes the corruption to cease when less than 158 columns
> are displayed.
(trimmin thr Cc list)

as a matter of fact i have been seeing the same problem also
on RELENG_6, on a desktop PC without powerd, and using an Intel
chipset with integrated video (i945 chipset) and the I810 driver:

	X Window System Version 7.2.0
	Release Date: 22 January 2007
	X Protocol Version 11, Revision 0, Release 7.2
	Build Operating System: FreeBSD 6.2-STABLE i386 

I seem to remember my laptop (Dell X300, i915 video card) also has
similar problems with wide xterms.

I believe the problem is in the i810 driver, or some interaction
with the system (agpgart) rather than related to powerd and CPU freq.

cheers
luigi

> Further investigation has unearthed that this problem happens only when
> the CPU frequency is set to low levels, which was happening because of
> powerd.  When the CPU frequency is set low, these pixel corruptions happen.
> When the CPU freq is raised they do not: everything is normal.
> 
> Disabling powerd and manually adjusting the CPU frequency gives these
results:
> 
> # sysctl dev.cpu.0.freq_levels
> dev.cpu.0.freq_levels: 3176/-1 2779/-1 2382/-1 1985/-1 1588/-1 1191/-1
794/-1 397/-1
> 
> CPU freq from 3176 to 1191 causes no problems.
> CPU freq at 794 or 397 causes pixel corruptions.
> 
> This problem did not happen on RELENG_6.
> 
> 	-jr