On Mon, Jan 27, 2020 at 05:17:01PM -0800, Yifeng Sun wrote: > Hi Ilya, > > Thanks for your reply. > > The thing is, if checksum offloading is enabled in both VMs, then > sender VM will send > a packet with invalid TCP checksum, and later OVS will send this > packet to receiver > VM directly without calculating a valid checksum. As a result, > receiver VM will drop > this packet because it contains invalid checksum. This is what > happened when I tried > this patch. >
When TSO is enabled, the TX checksumming offloading is required, then you will see invalid checksum. This is well documented here: https://github.com/openvswitch/ovs/blob/master/Documentation/topics/userspace-tso.rst#userspace-datapath---tso "Additionally, if the traffic is headed to a VM within the same host further optimization can be expected. As the traffic never leaves the machine, no MTU needs to be accounted for, and thus no segmentation and checksum calculations are required, which saves yet more cycles." Therefore, it's expected to see bad csum in the traffic dumps. To use the feature, you need few steps: enable the feature in OvS enable in qemu and inside the VM. The linux guest usually enable the feature by default if qemu offers it. HTH, fbl > Best, > Yifeng > > On Mon, Jan 27, 2020 at 12:09 PM Ilya Maximets <[email protected]> wrote: > > > > On 27.01.2020 18:24, Yifeng Sun wrote: > > > Hi Flavio, > > > > > > I am testing your patch using iperf between 2 VMs on the same host. > > > But it seems that TCP connection can't be created between these 2 VMs. > > > When inspecting further, I found that TCP packets have invalid checksums. > > > This might be the reason. > > > > > > I am wondering if I missed something in the setup? Thanks a lot. > > > > I didn't test myself, but according to current design, checksum offloading > > (rx and tx) shuld be enabled in both VMs. Otherwise all the packets will > > be dropped by the guest kernel. > > > > Best regards, Ilya Maximets. -- fbl _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
