On Wed, 19 Aug 2020 14:58:05 -0700
John Fastabend [off-list ref] wrote:
Jakub Kicinski wrote:
quoted
On Wed, 19 Aug 2020 22:22:23 +0200 Lorenzo Bianconi wrote:
quoted
quoted
On Wed, 19 Aug 2020 15:13:51 +0200 Lorenzo Bianconi wrote:
quoted
Enable the capability to receive jumbo frames even if the interface is
running in XDP mode
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Hm, already? Is all the infra in place? Or does it not imply
multi-buffer.
with this series mvneta supports xdp multi-buff on both rx and tx sides (XDP_TX
and ndo_xpd_xmit()) so we can remove MTU limitation.
Is there an API for programs to access the multi-buf frames?
Hi Lorenzo,
This is not enough to support multi-buffer in my opinion. I have the
same comment as Jakub. We need an API to pull in the multiple
buffers otherwise we break the ability to parse the packets and that
is a hard requirement to me. I don't want to lose visibility to get
jumbo frames.
At minimum we need a bpf_xdp_pull_data() to adjust pointer. In the
skmsg case we use this,
bpf_msg_pull_data(u32 start, u32 end, u64 flags)
Where start is the offset into the packet and end is the last byte we
want to adjust start/end pointers to. This way we can walk pages if
we want and avoid having to linearize the data unless the user actual
asks us for a block that crosses a page range. Smart users then never
do a start/end that crosses a page boundary if possible. I think the
same would apply here.
XDP by default gives you the first page start/end to use freely. If
you need to parse deeper into the payload then you call bpf_msg_pull_data
with the byte offsets needed.
I agree that we need a helper like this. (I also think Daniel have
proposed this before). This would also be useful for Eric Dumazet /
Google's header-split use-case[1]. As I understood from his talk[1],
the NIC HW might not always split the packet correctly (due to HW
limits). This helper could solve part of this challenge.
[1] https://netdevconf.info/0x14/session.html?talk-the-path-to-tcp-4k-mtu-and-rx-zerocopy
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer