Networking Configuration

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This page will host hints and tips pertaining to configuration of Linux and z/VM systems.


This section describes various problems and issues related to VSWITCH configuration and use.

QETH Buffer Count Parameter

By Ursala Braun - IBM: buffer_count determines the number of input buffers that the qeth driver shares with the (real or virtual) device. Every buffer is either controlled by Linux (when processing inbound data) or by the device (when providing inbound data). Initially Linux hands over control to the device for all available input buffers. The device fills (some of) them and notifies Linux. Now Linux controls these buffers, processes them, and returns control back to the device.

The device can provide inbound data only, if it controls at least 1 input buffer. That means, increasing the buffer_count increases the probability that the device controls input buffers to provide inbound data.

The maximum number of input buffers is 128. The only reason qeth chooses a default of 16 as buffer_count are memory-constrained systems. One buffer uses 64K of kernel memory. If your system is not memory-constrained and if the expected burst workload for your network connection is high, it makes always sense to increase buffer_count of a qeth device to 128. This applies to a VSWITCH-attached device as well.