Network I/O tuning
What we've seen in most KVM environments is that all the network traffic from a guest will take a single network path. There won't be any traffic segregation, which causes congestion in most KVM setups. As a first step for network tuning, we'd advise trying different networks or dedicated networks for management, backups, or live migration. But when you have more than one network interface for your traffic, please try to avoid multiple network interfaces for the same network or segment. If this is at all in play, apply some network tuning that is common for such setups; for example, use arp_filter to control ARP Flux. ARP Flux happens when a VM has more than one network interface and is using them actively to reply to ARP requests, so we should do the following:
echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter
After that, you need to edit /etc/sysctl.conf to make this setting persistent.