Changing buffer settings of the network interfaces

Edit online

In order to perform our WebSphere Application Server performance tests, we needed to change our buffer settings.

For our measurements, we made the following changes to our buffer settings:
  • The buffer count for our network connection was changed from 16 to 128.
  • The checksumming setting was changed from the default, software checksumming, to hardware checksumming.
    Note: For HiperSockets devices, hardware checksumming has no impact, because it does not provide the necessary hardware. Even when specified, checksumming will be done in software.

There is more than one way to change your buffer settings. Two methods are described below.

Method 1

We used the following steps to make our changes:
  • Take the devices down

    ifdown eth1

  • Take the devices offline

    echo 0 > /sys/bus/ccwgroup.drivers/qeth/0.0.0700/online

  • Change buffer count

    echo 128 > /sys/bus/ccwgroup/drivers/qeth/0.0.0700/buffer_count

  • Change checksumming

    echo hw_checksumming > /sys/bus/ccwgroup/drivers/qeth/0.0.0700/checksumming

  • Put devices back online

    echo 1 > /sys/bus/ccwgroup/drivers/qeth/0.0.0700/online

  • Restart the network

    service network restart

Method 2

The hardware configuration for qeth is found in the file “/etc/sysconfig/hardware/hwcfg-qeth-bus-ccw-0.0.nnnn “. Where “nnnn” is the device number of the appropriate network device.

We added the following line to change the number of buffers from 16, the default, to 128.

QETH_OPTIONS='checksumming=hw_checksumming buffer_count=128 '