On Thu, Aug 25, 2016 at 12:49 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > 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. > As I said the other thread, the better solution is to start tracking flows coming out of VMs.
Tom > > > >
