Setting the maximum buffer size

6.10 z/VM guest

Use the buffer attribute to set the maximum buffer size of an IUCV device.

About this task

The upper limit for the maximum buffer size is 32768␠bytes (32␠KB). The lower limit is 580 bytes in general and in addition, if the interface is up and running <current MTU + header size>. The header space is typically 4 bytes.

Changing the buffer size is accompanied by an mtu size change to the value <buffer size - header size>.

To set the maximum buffer size issue a command of this form:

# echo <value> > /sys/bus/iucv/drivers/netiucv/netiucv<n>/buffer

where:

<value>: is the number of bytes you want to set. If you specify a value outside the valid range, the command is ignored.
<n>: is an index that identifies the IUCV device and the corresponding interface.

Note: If IUCV performance deteriorates and IUCV issues out-of-memory messages on the console, consider using a buffer size less than 4K.

Example

In this example, the maximum buffer size of an IUCV device netiucv0 is set to 16384␠byte.

# echo 16384 > /sys/bus/iucv/drivers/netiucv/netiucv0/buffer