From KVM

Windows registry settings

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.

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