Querying the HPF setting of a channel path

Red Hat Enterprise Linux 9.2 LPAR mode z/VM guest KVM guest

Query the High Performance FICON® (HPF) state of a channel path through the hpf sysfs attribute. The HPF function can be lost if the device cannot provide the function, or if the channel path is not able to do HPF.

About this task

The HPF channel-path is deactivated if an HPF error occurs indicating that HPF is not available if there are other channel paths available. If no other channel paths are available, the path remains operational with HPF deactivated.

If the device loses HPF functionality, HPF is disabled for all channel paths defined for the device.

Procedure

High Performance FICON for a device is available if the hpf sysfs attribute is 1, and unavailable otherwise.

To query the HPF function for a channel path, issue a command of this form:

# lsdasd -l <device_bus_id>

Alternatively, you can query the sysfs attribute directly:

# cat /sys/bus/ccw/devices/<device_bus_id>/hpf

where /sys/bus/ccw/devices/<device_bus_id> represents the device in sysfs.

Example

To query the availability of HPF for a device 0.0.4711, issue:

lsdasd -l 0.0.4711

0.0.4711/dasdc/94:8
  status:                           active
  type:                             ECKD
  ...                               ...
  hpf:                              1

This example indicates that HPF is enabled for the device.

Alternatively, read from the hpf sysfs attribute:

cat /sys/bus/ccw/devices/0.0.4712/hpf
0

This example indicates that HPF is disabled for device 0.0.4712.

What to do next

You can now reset the paths to the device. You can use the tunedasd command to reset all or one channel path.

To re-validate all paths for one device and if possible reset HPF:

# tunedasd --path_reset_all /dev/dasdc
Resetting all chpids for device </dev/dasdc>...
Done.

See tunedasd - Adjust low-level DASD settings for details.

You can also use sysfs to reset a path. sysfs expects a path mask. For example to reset CHPID 44, you can use tunedasd:

tunedasd -p 44 /dev/dasde

This would be the same as specifying the following in sysfs:

echo 08 > /sys/bus/ccw/devices/0.0.9330/path_reset

Both commands will reset CHPID 44 (path mask 08).