Messages in this thread | | | Subject | Re: [PATCH net-next 0/2] virtio-net: re enable XDP_REDIRECT for mergeable buffer | From | Jason Wang <> | Date | Thu, 1 Mar 2018 21:15:36 +0800 |
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On 2018年03月01日 18:35, Jesper Dangaard Brouer wrote: > On Thu, 1 Mar 2018 17:23:37 +0800 > Jason Wang <jasowang@redhat.com> wrote: > >> On 2018年03月01日 17:10, Jesper Dangaard Brouer wrote: >>> On Thu, 1 Mar 2018 11:19:03 +0800 >>> Jason Wang <jasowang@redhat.com> wrote: >>> >>>> This series tries to re-enable XDP_REDIRECT for mergeable buffer which >>>> was removed since commit 7324f5399b06 ("virtio_net: disable >>>> XDP_REDIRECT in receive_mergeable() case"). Main concerns are: >>>> >>>> - not enough tailroom was reserved which breaks cpumap >>> To address this at a more fundamental level, I would suggest that we/you >>> instead extend XDP to know it's buffers "frame" size/end. (The >>> assumption use to be, xdp_buff->data_hard_start + PAGE_SIZE, but >>> ixgbe+virtio_net broke that assumption). >>> >>> It should actually be fairly easy to implement: >>> * Simply extend xdp_buff with a "data_hard_end" pointer. >> Right, and then cpumap can warn and drop packets with insufficient >> tailroom. >> >> But it should be a patch on top of this I think. > Hmmm, not really. If we/you instead fix the issue of XDP doesn't know > the end/size of the frame, then we don't need this mixed XDP > generic/native code path mixing.
I know this but I'm still a little bit confused. According to the commit log of 7324f5399b06 ("virtio_net: disable XDP_REDIRECT in receive_mergeable() case"), you said:
""" The longer explaination is that receive_mergeable() tries to work-around and satisfy these XDP requiresments e.g. by having a function xdp_linearize_page() that allocates and memcpy RX buffers around (in case packet is scattered across multiple rx buffers). This does currently satisfy XDP_PASS, XDP_DROP and XDP_TX (but only because we have not implemented bpf_xdp_adjust_tail yet). """
So I consider the tailroom is a must for the (future) tail adjustment.
> > You could re-enable native redirect, and push the responsibility to > cpumap for detecting this too-small frame "missing tailroom" (and avoid > crashing...). (If we really want to support this, cpumap could fallback > to dev_alloc_skb, and handle it gracefully). >
Right but it will be slower than build_skb().
Thanks
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