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Re: Minimal performance gain with jumbo frames (MTU 9000) during VM migration



Good morning Mario, 

Usually Jumbo Frames will lead you to lower CPU usage for the same heavy workload, not more throughput.

What's the throughput you are seen on those ports?.

Regards,
CI

On Tue, Oct 7, 2025, 11:52 Mario V. Guenzi <jclark@xxxxxxxxxx> wrote:

Hi everyone,

I'm trying to configure jumbo frames on two cluster nodes running Xen 4.17.
Both nodes are on Devuan 5, and the NICs are Intel Corporation Ethernet Controller 10-Gigabit X540-AT2.

At boot, I apply the following MTU settings:

post-up ifconfig eth05 mtu 9000 && ifconfig eth07 mtu 9000 && ifconfig bond1 mtu 9000

The two NICs are bonded with these settings:

bond-slaves eth05 eth07 bond-primary eth05 bond-mode 0 bond-miimon 100 bond-updelay 200 bond-downdelay 200

In rc.local I enable the following offload options:

ethtool -K eth05 rx on ethtool -K eth05 tx on ethtool -K eth05 sg on ethtool -K eth05 tso on ethtool -K eth05 gso on ethtool -K eth05 gro off

Sysctl/kernel network tuning parameters:

net.core.somaxconn = 1000 net.core.netdev_max_backlog = 300000 net.core.rmem_max = 16777216 net.core.wmem_max = 16777216 net.ipv4.tcp_max_syn_backlog = 8096 net.ipv4.tcp_slow_start_after_idle = 0 net.ipv4.tcp_tw_reuse = 1 net.ipv4.ip_local_port_range = 10240 65535 net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 65536 16777216 net.ipv4.tcp_mtu_probing = 1 net.ipv4.route.flush = 1 net.ipv4.tcp_timestamps = 0 net.ipv4.tcp_fin_timeout = 15 net.ipv4.tcp_sack = 0 net.ipv4.tcp_moderate_rcvbuf = 1 vm.vfs_cache_pressure = 50

The issue:
When I perform a VM live migration between the two nodes, the difference between MTU 1500 and 9000 is negligible—only about 2–3 seconds faster with jumbo frames enabled.

Does anyone know what I might be missing or doing wrong?
Any tips or insights would be greatly appreciated.

Thanks in advance and best regards



-- 
 
Mario Vittorio Guenzi
E-mail jclark@xxxxxxxxxx
Si vis pacem, para bellum

 


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