### Performance Tuning: Latency

Use this information to check or change the driver latency settings.

#### Driver Modes

The AIX device driver may be configured to operate in two modes, polled mode or interrupt mode. The poll or interrupt interval is also configurable. These parameters are alterable on a per-adapter basis.

Note: The operational mode and the poll/interrupt interval are not configurable using the AIX System Management Interface Tool (SMIT). They may only be altered by directly manipulating the adapter attributes in the AIX device database. See Configuring Operational Mode and Poll/Interrupt Interval below.

##### Polled Mode

This mode is the default for the driver. When polled mode is selected, the driver queries the adapter for received data and communications events at periodic intervals. The polling interval may be configured in 10-ms increments. The minimum interval is 10-ms.

##### Interrupt Mode

When interrupt mode is selected, the adapter will interrupt the driver when received data is available or communications events occur. The interrupt value may be configured in 1-ms increments. The minimum interrupt interval is 1-ms. Interrupts are generated with a period not to exceed the specified value.

#### Procedure: Checking the Current Settings

The following command will display the current values of latency settings:

`lsattr -E -l dm0`

`dm0` is used here as an example. Substitute your adapter name for `dm0`. Use this command to identify your adapter name.

`lsdev -Cc adapter`

If the poll_flag attribute is true, polling mode is enabled. If the poll_flag attribute is false, interrupt mode is enabled. The default value is true.

The poll or interrupt interval is specified by the poll_value attribute. The default value is 15-ms. (Because of system constraints, a 15-ms polling interval is effectively 10-ms).

#### Procedure: Configuring Operational Mode and Poll/Interrupt Interval

To change the poll_flag and/or the poll_value, do the following:

1. Access a root prompt on the AIX system.
2. Use the 'lsdev -Cc adapter' command to identify the adapter name.
3. Close all devices on the adapter.
4. Change the state of the adapter from Available to Defined with this command:

   `rmdev -R -l dm0`

   dm0 is used here as an example. Substitute your adapter name for dm0.

5. Change the poll_flag and poll_value attribute(s) as needed with the chdev command:

   Example:

   `chdev -l dm0 -a poll_flag=false`

   `chdev -l dm0 -a poll_value=5`

   This example changes the operational mode to interrupt (poll_flag=false) and sets the minimum interrupt interval (poll_value=5) to 5-ms.

6. Restore the adapter state to Available with this command:

   `cfgmgr -l dm0`