How to Disable Receive-Side Copy (RSC) in Dom0

Summary

This article describes how to disable Receive-Side Copy in dom0.

Receive-Side Copy (RSC) might cause exhaustion of dom0 pageref resources. This might lead to undesirable behavior under certain circumstances.

Requirements

RSC as the default network back end.

Background

By default, xen_netback.netback_max_rx_protocol is set to 1, which enables RSC host wide.

Procedure

Run the following command:
#/opt/xensource/libexec/xen-cmdline --set-dom0 xen_netback.netback_max_rx_protocol=0
Restart the server for the change to take effect.
Confirm that the change has been implemented:
# cat /proc/cmdline
root=LABEL=root-cbscvkzh ro console=tty0 xencons=hvc console=hvc0 xen_netback.netback_max_rx_protocol=0

Throughput should not be adversely affected by turning RSC off. It is likely to put more CPU load on Dom0, depending upon the volume of network traffic and amount of Virtual Machines.

More Information

CTX133199 – How to Disable Receive-Side Copy (RSC) on XenServer 6.x
RSC and the Impact on XenServer Scalability