WindowsGuestDrivers/kvmnet/registry
From KVM
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
Additional links
Windows Sockets and DNS Registry Parameters Server Does Not Use All Bandwidth Available When Streaming Files with Bit Rates over 100 Kbps