Re: [PATCH bpf-next v2 0/3] xsk: build skb by page

* Re: [PATCH bpf-next v2 0/3] xsk: build skb by page
       [not found] <cover.1611048724.git.xuanzhuo@linux.alibaba.com>
@ 2021-01-19  9:50 ` Michael S. Tsirkin
       [not found]   ` <1611053609.502882-1-xuanzhuo@linux.alibaba.com>
       [not found] ` <30ae1c94b5c26919bd90bb251761c526edfbaf56.1611048724.git.xuanzhuo@linux.alibaba.com>
  1 sibling, 1 reply; 3+ messages in thread
From: Michael S. Tsirkin @ 2021-01-19  9:50 UTC (permalink / raw)
  To: Xuan Zhuo
  Cc: Song Liu, Martin KaFai Lau, Jesper Dangaard Brouer,
	Daniel Borkmann, netdev, John Fastabend, Alexei Starovoitov,
	Andrii Nakryiko, Yonghong Song, Jonathan Lemon, KP Singh,
	Jakub Kicinski, bpf, Björn Töpel, virtualization,
	David S. Miller, Magnus Karlsson

On Tue, Jan 19, 2021 at 05:45:09PM +0800, Xuan Zhuo wrote:
> v2:
>     1. add priv_flags IFF_TX_SKB_NO_LINEAR instead of netdev_feature
>     2. split the patch to three:
>         a. add priv_flags IFF_TX_SKB_NO_LINEAR
>         b. virtio net add priv_flags IFF_TX_SKB_NO_LINEAR
>         c. When there is support this flag, construct skb without linear space
>     3. use ERR_PTR() and PTR_ERR() to handle the err
> 
> 
> v1 message log:
> ---------------
> 
> This patch is used to construct skb based on page to save memory copy
> overhead.
> 
> This has one problem:
> 
> We construct the skb by fill the data page as a frag into the skb. In
> this way, the linear space is empty, and the header information is also
> in the frag, not in the linear space, which is not allowed for some
> network cards. For example, Mellanox Technologies MT27710 Family
> [ConnectX-4 Lx] will get the following error message:
> 
>     mlx5_core 0000:3b:00.1 eth1: Error cqe on cqn 0x817, ci 0x8, qn 0x1dbb, opcode 0xd, syndrome 0x1, vendor syndrome 0x68
>     00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000030: 00 00 00 00 60 10 68 01 0a 00 1d bb 00 0f 9f d2
>     WQE DUMP: WQ size 1024 WQ cur size 0, WQE index 0xf, len: 64
>     00000000: 00 00 0f 0a 00 1d bb 03 00 00 00 08 00 00 00 00
>     00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000020: 00 00 00 2b 00 08 00 00 00 00 00 05 9e e3 08 00
>     00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     mlx5_core 0000:3b:00.1 eth1: ERR CQE on SQ: 0x1dbb
> 
> I also tried to use build_skb to construct skb, but because of the
> existence of skb_shinfo, it must be behind the linear space, so this
> method is not working. We can't put skb_shinfo on desc->addr, it will be
> exposed to users, this is not safe.
> 
> Finally, I added a feature NETIF_F_SKB_NO_LINEAR to identify whether the
> network card supports the header information of the packet in the frag
> and not in the linear space.
> 
> ---------------- Performance Testing ------------
> 
> The test environment is Aliyun ECS server.
> Test cmd:
> ```
> xdpsock -i eth0 -t  -S -s <msg size>
> ```
> 
> Test result data:
> 
> size    64      512     1024    1500
> copy    1916747 1775988 1600203 1440054
> page    1974058 1953655 1945463 1904478
> percent 3.0%    10.0%   21.58%  32.3%

Just making sure, are these test results with v2?

> 
> Xuan Zhuo (3):
>   net: add priv_flags for allow tx skb without linear
>   virtio-net: support IFF_TX_SKB_NO_LINEAR
>   xsk: build skb by page
> 
>  drivers/net/virtio_net.c  |   3 +-
>  include/linux/netdevice.h |   3 ++
>  net/xdp/xsk.c             | 112 ++++++++++++++++++++++++++++++++++++++--------
>  3 files changed, 99 insertions(+), 19 deletions(-)
> 
> --
> 1.8.3.1

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