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@xxxxxxxxxx> 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@xxxxxxxxxx> 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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