> On 19 Mar 2019, at 23:06, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Tue, Mar 19, 2019 at 02:38:06PM +0200, Liran Alon wrote: >> Hi Michael, >> >> Great blog-post which summarise everything very well! >> >> Some comments I have: > > Thanks! > I'll try to update everything in the post when I'm not so jet-lagged. > >> 1) I think that when we are using the term “1-netdev model” on community discussion, we tend to refer to what you have defined in blog-post as "3-device model with hidden slaves”. >> Therefore, I would suggest to just remove the “1-netdev model” section and rename the "3-device model with hidden slaves” section to “1-netdev model”. >> >> 2) The userspace issues result both from using “2-netdev model” and “3-netdev model”. However, they are described in blog-post as they only exist on “3-netdev model”. >> The reason these issues are not seen in Azure environment is because these issues were partially handled by Microsoft for their specific 2-netdev model. >> Which leads me to the next comment. >> >> 3) I suggest that blog-post will also elaborate on what exactly are the userspace issues which results in models different than “1-netdev model”. >> The issues that I’m aware of are (Please tell me if you are aware of others!): >> (a) udev rename race-condition: When net-failover device is opened, it also opens it's slaves. However, the order of events to udev on KOBJ_ADD is first for the net-failover netdev and only then for the virtio-net netdev. This means that if userspace will respond to first event by open the net-failover, then any attempt of userspace to rename virtio-net netdev as a response to the second event will fail because the virtio-net netdev is already opened. Also note that this udev rename rule is useful because we would like to add rules that renames virtio-net netdev to clearly signal that it’s used as the standby interface of another net-failover netdev. >> The way this problem was workaround by Microsoft in NetVSC is to delay the open done on slave-VF from the open of the NetVSC netdev. However, this is still a race and thus a hacky solution. It was accepted by community only because it’s internal to the NetVSC driver. However, similar solution was rejected by community for the net-failover driver. >> The solution that we currently proposed to address this (Patch by Si-Wei) was to change the rename kernel handling to allow a net-failover slave to be renamed even if it is already opened. Patch is still not accepted. >> (b) Issues caused because of various userspace components DHCP the net-failover slaves: DHCP of course should only be done on the net-failover netdev. Attempting to DHCP on net-failover slaves as-well will cause networking issues. Therefore, userspace components should be taught to avoid doing DHCP on the net-failover slaves. The various userspace components include: >> b.1) dhclient: If run without parameters, it by default just enum all netdevs and attempt to DHCP them all. >> (I don’t think Microsoft has handled this) >> b.2) initramfs / dracut: In order to mount the root file-system from iSCSI, these components needs networking and therefore DHCP on all netdevs. >> (Microsoft haven’t handled (b.2) because they don’t have images which perform iSCSI boot in their Azure setup. Still an open issue) >> b.3) cloud-init: If configured to perform network-configuration, it attempts to configure all available netdevs. It should avoid however doing so on net-failover slaves. >> (Microsoft has handled this by adding a mechanism in cloud-init to blacklist a netdev from being configured in case it is owned by a specific PCI driver. Specifically, they blacklist Mellanox VF driver. However, this technique doesn’t work for the net-failover mechanism because both the net-failover netdev and the virtio-net netdev are owned by the virtio-net PCI driver). >> b.4) Various distros network-manager need to be updated to avoid DHCP on net-failover slaves? (Not sure. Asking...) >> >> 4) Another interesting use-case where the net-failover mechanism is useful is for handling NIC firmware failures or NIC firmware Live-Upgrade. >> In both cases, there is a need to perform a full PCIe reset of the NIC. Which lose all the NIC eSwitch configuration of the various VFs. > > In this setup, how does VF keep going? If it doesn't keep going, why is > it helpful? Let me attempt to clarify. First, let’s analyse what can a cloud provider do when it wishes to upgrade the NIC firmware when there are currently running guests utilising SR-IOV. He can perform the following operations in order: 1) Hot-unplug all VFs from all running guests. 2) Upgrade NIC firmware. Will result in PCIe reset which will cause momentary network down-time on PF but immediately afterwards PF will be set up again and guests will have network connectivity. 3) Provision and hot-plug new VFs for all running guests. Guests again have accelerated networking. Without the net-failover mechanism, host will have to hot-unplug all VFs from all running guests and provision new VFs and hot-plug them anyway. But in that case, the network down-time for guests is longer. Second, let’s analyse what will happen when health service running on host notice that NIC firmware is in a bad state and therefore NIC should be reset to recover. The health service can take exactly the same order of operations as described above besides (2) which will just become a PCIe reset. Again, guests have shorter network down-time in this case as-well when utilising the net-failover mechanism. > >> To handle these cases gracefully, one could just hot-unplug all VFs from guests running on host (which will make all guests now use the virtio-net netdev which is backed by a netdev that eventually is on top of PF). Therefore, networking will be restored to guests once the PCIe reset is completed and the PF is functional again. To re-acceelrate the guests network, hypervisor can just hot-plug new VFs to guests. >> >> P.S: >> I would very appreciate all this forum help in closing on the pending items written in (3). Which currently prevents using this net-failover mechanism in real production use-cases. >> >> Regards, >> -Liran >> >>> On 17 Mar 2019, at 15:55, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: >>> >>> Hi all, >>> I've put up a blog post with a summary of where network >>> device failover stands and some open issues. >>> Not sure where best to host it, I just put it up on blogspot: >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__mstsirkin.blogspot.com_2019_03_virtio-2Dnetwork-2Ddevice-2Dfailover-2Dsupport.html&d=DwIBAg&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=jd0emHx6EkPSTvO0TytfYmG4rOMQ9htenhrgKprrh9E&s=5EJamlc_g1lZa0Ga7K30E6aWVg3jy8lizhw1aSguo3A&e= >>> >>> Comments, corrections are welcome! >>> >>> -- >>> MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
