Low CPU Freq responsible for xterm pixel corruption on RELENG_7

J.R. Oldroyd fbsd at opal.com
Sun Jan 27 17:54:06 PST 2008

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:

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.

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