WindowsGuestDrivers/kvmnet/registry

This page describes best practice for configuring Windows TCP\IP related parameters to archive the best performance with Windows guests. Those parameters are unrelated to kvm\VirtIO drivers , rather general Windows settings. After changing those setting reboot is required for the changes to effect the system.

Windows XP and 2003 registry settings

Registry settings

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\AFD\Parameters]

"DefaultSendWindow"=dword:00100000

"DefaultReceiveWindow"=dword:00100000

"FastSendDatagramThreshold"=dword:00004000

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]

"Tcp1323Opts"=dword:00000001

"TcpWindowSize"=dword:00100000

• Tcp1323Opts - allows the scaling of the TCP window above 16k. For more info read Tcp1323Opts
• "DefaultSendWindow", "DefaultReceiveWindow" and "TcpWindowSize" control TCP window size
• "FastSendDatagramThreshold" - controls fast UDP transmit.

Additional links

• Windows Sockets and DNS Registry Parameters
• Server Does Not Use All Bandwidth Available When Streaming Files with Bit Rates over 100 Kbps