On 11/21/19 11:09 PM, Jason Wang wrote: >> Doubling the number of queues for each tap device adds overhead to the >> hypervisor if you only want to allow XDP_DROP or XDP_DIRECT. Am I >> understanding that correctly? > > > Yes, but there's almost impossible to know whether or not XDP_TX will be > used by the program. If we don't use per CPU TX queue, it must be > serialized through locks, not sure it's worth try that (not by default, > of course). > This restriction is going to prevent use of XDP in VMs in general cloud hosting environments. 2x vhost threads for vcpus is a non-starter. If one XDP feature has high resource needs, then we need to subdivide the capabilities to let some work and others fail. For example, a flag can be added to xdp_buff / xdp_md that indicates supported XDP features. If there are insufficient resources for XDP_TX, do not show support for it. If a program returns XDP_TX anyways, packets will be dropped.
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