Re: [PATCH bpf-next 0/5] Add support for SKIP_BPF flag for AF_XDP sockets

["Björn Töpel" <bjorn.topel@intel.com>]

On 2019-08-15 05:46, Sridhar Samudrala wrote:
> This patch series introduces XDP_SKIP_BPF flag that can be specified
> during the bind() call of an AF_XDP socket to skip calling the BPF
> program in the receive path and pass the buffer directly to the socket.
> 
> When a single AF_XDP socket is associated with a queue and a HW
> filter is used to redirect the packets and the app is interested in
> receiving all the packets on that queue, we don't need an additional
> BPF program to do further filtering or lookup/redirect to a socket.
> 
> Here are some performance numbers collected on
>    - 2 socket 28 core Intel(R) Xeon(R) Platinum 8180 CPU @ 2.50GHz
>    - Intel 40Gb Ethernet NIC (i40e)
> 
> All tests use 2 cores and the results are in Mpps.
> 
> turbo on (default)
> ---------------------------------------------	
>                        no-skip-bpf    skip-bpf
> ---------------------------------------------	
> rxdrop zerocopy           21.9         38.5
> l2fwd  zerocopy           17.0         20.5
> rxdrop copy               11.1         13.3
> l2fwd  copy                1.9          2.0
> 
> no turbo :  echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo
> ---------------------------------------------	
>                        no-skip-bpf    skip-bpf
> ---------------------------------------------	
> rxdrop zerocopy           15.4         29.0
> l2fwd  zerocopy           11.8         18.2
> rxdrop copy                8.2         10.5
> l2fwd  copy                1.7          1.7
> ---------------------------------------------	
>

This work is somewhat similar to the XDP_ATTACH work [1]. Avoiding the
retpoline in the XDP program call is a nice performance boost! I like
the numbers! :-) I also like the idea of adding a flag that just does
what most AF_XDP Rx users want -- just getting all packets of a
certain queue into the XDP sockets.

In addition to Toke's mail, I have some more concerns with the series:

* AFAIU the SKIP_BPF only works for zero-copy enabled sockets. IMO, it
   should work for all modes (including XDP_SKB).

* In order to work, a user still needs an XDP program running. That's
   clunky. I'd like the behavior that if no XDP program is attached,
   and the option is set, the packets for a that queue end up in the
   socket. If there's an XDP program attached, the program has
   precedence.

* It requires changes in all drivers. Not nice, and scales badly. Try
   making it generic (xdp_do_redirect/xdp_flush), so it Just Works for
   all XDP capable drivers.

Thanks for working on this!


Björn

[1] 
https://lore.kernel.org/netdev/20181207114431.18038-1-bjorn.topel@gmail.com/


> Sridhar Samudrala (5):
>    xsk: Convert bool 'zc' field in struct xdp_umem to a u32 bitmap
>    xsk: Introduce XDP_SKIP_BPF bind option
>    i40e: Enable XDP_SKIP_BPF option for AF_XDP sockets
>    ixgbe: Enable XDP_SKIP_BPF option for AF_XDP sockets
>    xdpsock_user: Add skip_bpf option
> 
>   drivers/net/ethernet/intel/i40e/i40e_txrx.c   | 22 +++++++++-
>   drivers/net/ethernet/intel/i40e/i40e_xsk.c    |  6 +++
>   drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 20 ++++++++-
>   drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c  | 16 ++++++-
>   include/net/xdp_sock.h                        | 21 ++++++++-
>   include/uapi/linux/if_xdp.h                   |  1 +
>   include/uapi/linux/xdp_diag.h                 |  1 +
>   net/xdp/xdp_umem.c                            |  9 ++--
>   net/xdp/xsk.c                                 | 43 ++++++++++++++++---
>   net/xdp/xsk_diag.c                            |  5 ++-
>   samples/bpf/xdpsock_user.c                    |  8 ++++
>   11 files changed, 135 insertions(+), 17 deletions(-)
>