On Thu, 2016-08-25 at 12:23 -0700, Alexander Duyck wrote: > I have been seeing a number of issues where XPS leads to issues with > packets being reordered in the transmit queues of the device drivers. The > main situation where this seems to occur is when a VM us using a tap > interface to send packets to the network via a NIC that has XPS enabled. > > A bit of looking into this revealed the main issue is that the scheduler > seems to be migrating the VM between CPUs and as this occurs the traffic > for a given flow from a VM is following this migration and hopping between > Tx queues leading to packet reordering. > > A workaround for this is to make certain all the VMs have RPS enabled on > the tap interfaces, however this requires extra configuration on the host > for each VM created. > > A simpler approach is provided with this patch. With it we disable XPS any > time a socket is not present for a given flow. By doing this we can avoid > using XPS for any routing or bridging situations in which XPS is likely > more of a hinderance than a help.
Yes, but this will destroy isolation for people properly doing VM cpu pining. With this patch, DDOS traffic coming from a VM will hit all TX queues.
