Setting the 3215 line-mode terminal mode for handling a full console buffer
A full console buffer might result from processes that issue console output faster than the 3215 line-mode terminal device driver can process it. Possible responses to this condition are slowing operations or dropping console output.
As of kernel 6.2, the default behavior of the 3215 line-mode terminal device driver is to drop console output rather than slowing down Linux®.
Use the con3215_drop= kernel parameter to restore the traditional behavior.
Traditionally, the device driver displays output until the screen is full. No further data is then
displayed until the operator presses a clear key or until a timeout interval expires. For more
information about the con3215_drop= kernel parameter, see Console kernel parameter syntax.
On a running Linux instance, the
/sys/bus/ccw/drivers/3215/con3215_drop sysfs attribute governs how the 3215
line-mode terminal device driver handles a full console buffer. Read the attribute to find out the
current setting. Write 0 or 1 to the attribute to change the setting.
- 1
- avoids pauses by overwriting used output buffer pages, even if the content was never written to an output device.
- 0
- assures complete console output by pausing until used output buffer pages are written to an output device and can be reused without loss.
Example: In this example, the initial setting favors speed over
completeness. This setting is then changed to assure complete console output at the expense of
speed.
# cat /sys/bus/ccw/drivers/3215/con3215_drop 1 # echo 0 > /sys/bus/ccw/drivers/3215/con3215_drop