Wednesday, February 1, 2017

How to enable or disable offload features like TSO, GSO, SG, TX/RX Checksum

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TCP offload engine or TOE is a technology used in network interface cards (NIC) to offload processing of the entire TCP/IP stack to the network controller. It is primarily used with high-speed network interfaces, such as gigabit Ethernet and 10 Gigabit Ethernet, where processing overhead of the network stack becomes significant.

Usually when a packet arrives at network interface, it sends a hard interrupt to the processor. So depends up on the traffic, processor has to work more, handle the interrupts, calculate and compare the checksum etc. This will increase the load on CPU.

So a lot of modern Ethernet cards comes up with inbuilt support for checking checksum, handling errors etc. Enabling this we can reduce some load on the CPU.

First we need to check what are features enabled on the interface. They will be shown as On or Off. They may ne associated with a [fixed] parameter which says the value is fixed and we cannot change it.

[root@sysadmin ~]# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:24:21:A5:75:55
          inet addr:192.168.1.254  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::224:21ff:fea5:7555/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:144736 errors:0 dropped:0 overruns:0 frame:0
          TX packets:107522 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:134934140 (128.6 MiB)  TX bytes:11959446 (11.4 MiB)

[root@sysadmin ~]# ethtool --show-offload  eth0
Features for eth0:
rx-checksumming: on
tx-checksumming: off
        tx-checksum-ipv4: off
        tx-checksum-unneeded: off [fixed]
        tx-checksum-ip-generic: off [fixed]
        tx-checksum-ipv6: off [fixed]
        tx-checksum-fcoe-crc: off [fixed]
        tx-checksum-sctp: off [fixed]
scatter-gather: off
        tx-scatter-gather: off
        tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: off
        tx-tcp-segmentation: off
        tx-tcp-ecn-segmentation: off [fixed]
        tx-tcp6-segmentation: off [fixed]
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: off [requested on]
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: off [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
fcoe-mtu: off [fixed]
loopback: off [fixed]

We can set the tx checksumming using the following command:
[root@sysadmin ~]# ethtool --offload  eth0  rx on  tx on
[root@sysadmin ~]# ethtool --show-offload  eth0
Features for eth0:
rx-checksumming: on
tx-checksumming: on
        tx-checksum-ipv4: on
        tx-checksum-unneeded: off [fixed]
        tx-checksum-ip-generic: off [fixed]
        tx-checksum-ipv6: off [fixed]
        tx-checksum-fcoe-crc: off [fixed]
        tx-checksum-sctp: off [fixed]
scatter-gather: off
        tx-scatter-gather: off
        tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: off
        tx-tcp-segmentation: off
        tx-tcp-ecn-segmentation: off [fixed]
        tx-tcp6-segmentation: off [fixed]
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: off [requested on]
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: off [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
fcoe-mtu: off [fixed]
loopback: off [fixed]
[root@sysadmin ~]#

We can enable scatter-gather using the following command:
[root@sysadmin ~]# ethtool --offload  eth0 sg on
[root@sysadmin ~]# ethtool --show-offload  eth0
Features for eth0:
rx-checksumming: on
tx-checksumming: on
        tx-checksum-ipv4: on
        tx-checksum-unneeded: off [fixed]
        tx-checksum-ip-generic: off [fixed]
        tx-checksum-ipv6: off [fixed]
        tx-checksum-fcoe-crc: off [fixed]
        tx-checksum-sctp: off [fixed]
scatter-gather: on
        tx-scatter-gather: on
        tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
        tx-tcp-segmentation: on
        tx-tcp-ecn-segmentation: off [fixed]
        tx-tcp6-segmentation: off [fixed]
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: off [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
fcoe-mtu: off [fixed]
loopback: off [fixed]

We can eable TSO (TCP Segmentation offload) using the following command:
[root@sysadmin ~]# ethtool --offload eth0 tso on
[root@sysadmin ~]# ethtool --show-offload  eth0
Features for eth0:
rx-checksumming: on
tx-checksumming: on
        tx-checksum-ipv4: on
        tx-checksum-unneeded: off [fixed]
        tx-checksum-ip-generic: off [fixed]
        tx-checksum-ipv6: off [fixed]
        tx-checksum-fcoe-crc: off [fixed]
        tx-checksum-sctp: off [fixed]
scatter-gather: on
        tx-scatter-gather: on
        tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
        tx-tcp-segmentation: on
        tx-tcp-ecn-segmentation: off [fixed]
        tx-tcp6-segmentation: off [fixed]
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: off [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
fcoe-mtu: off [fixed]
loopback: off [fixed]
[root@sysadmin ~]#

You can enable GSO(Generic Segmentation Offload) using the following command:
[root@sysadmin ~]# ethtool --offload  eth0 gso on
[root@sysadmin ~]# ethtool --show-offload  eth0
Features for eth0:
rx-checksumming: on
tx-checksumming: on
        tx-checksum-ipv4: on
        tx-checksum-unneeded: off [fixed]
        tx-checksum-ip-generic: off [fixed]
        tx-checksum-ipv6: off [fixed]
        tx-checksum-fcoe-crc: off [fixed]
        tx-checksum-sctp: off [fixed]
scatter-gather: on
        tx-scatter-gather: on
        tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
        tx-tcp-segmentation: on
        tx-tcp-ecn-segmentation: off [fixed]
        tx-tcp6-segmentation: off [fixed]
udp-fragmentation-offload: off [fixed]
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: on
tx-vlan-offload: on
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: off [fixed]
rx-vlan-filter: off [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: off [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
fcoe-mtu: off [fixed]
loopback: off [fixed]

References:
1. https://en.wikipedia.org/wiki/TCP_offload_engine 
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