On 2019/11/22 下午11:43, David Ahern wrote:
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.
Or we can just: - If queues is sufficient, using per-cpu TX queue- If not, synchronize through spinlocks (like what TAP did right now, since there's no easy way to have more queues on the fly)
Thanks
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