Low CPU Freq responsible for xterm pixel corruption on RELENG_7

Luigi Rizzo luigi at onelab2.iet.unipi.it
Sun Jan 27 18:28:20 PST 2008

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.


> 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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