Channel path measurement

A sysfs attribute controls the channel path measurement facility of the channel subsystem.

/sys/devices/css0/cm_enable
With the cm_enable attribute you can enable and disable the extended channel-path measurement facility. It can take the following values:
0
Deactivates the measurement facility and remove the measurement-related attributes for the channel paths. No action if measurements are not active.
1
Attempts to activate the measurement facility and create the measurement-related attributes for the channel paths. No action if measurements are already active.
If a machine does not support extended channel-path measurements the cm_enable attribute is not created.
Two sysfs attributes are added for each channel path object:
cmg
Specifies the channel measurement group or unknown if no characteristics are available.
shared
Specifies whether the channel path is shared between LPARs or unknown if no characteristics are available.
If measurements are active, two more sysfs attributes are created for each channel path object:
measurement
A binary sysfs attribute that contains the extended channel-path measurement data for the channel path. It consists of eight 32-bit values and must always be read in its entirety, or 0 will be returned.
measurement_chars
A binary sysfs attribute that is either empty, or contains the channel measurement group dependent characteristics for the channel path, if the channel measurement group is 2 or 3. If not empty, it consists of five 32-bit values.

Examples

  • To turn measurements on issue: 
    # echo 1 > /sys/devices/css0/cm_enable
  • To turn measurements off issue: 
    # echo 0 > /sys/devices/css0/cm_enable