[Intel-wired-lan] [PATCH bpf-next 0/5] Add support for SKIP_BPF flag for AF_XDP sockets
Jonathan Lemon
jonathan.lemon at gmail.com
Fri Aug 16 22:08:34 UTC 2019
On 16 Aug 2019, at 6:32, Björn Töpel wrote:
> On Thu, 15 Aug 2019 at 18:46, Samudrala, Sridhar
> <sridhar.samudrala at intel.com> wrote:
>>
>> On 8/15/2019 5:51 AM, Björn Töpel wrote:
>>> 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).
>>
>> This patch enables SKIP_BPF for AF_XDP sockets where an XDP program
>> is
>> attached at driver level (both zerocopy and copy modes)
>> I tried a quick hack to see the perf benefit with generic XDP mode,
>> but
>> i didn't see any significant improvement in performance in that
>> scenario. so i didn't include that mode.
>>
>>>
>>> * 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.
>>
>> I think this would require more changes in the drivers to take XDP
>> datapath even when there is no XDP program loaded.
>>
>
> Today, from a driver perspective, to enable XDP you pass a struct
> bpf_prog pointer via the ndo_bpf. The program get executed in
> BPF_PROG_RUN (via bpf_prog_run_xdp) from include/linux/filter.h.
>
> I think it's possible to achieve what you're doing w/o *any* driver
> modification. Pass a special, invalid, pointer to the driver (say
> (void *)0x1 or smth more elegant), which has a special handling in
> BPF_RUN_PROG e.g. setting a per-cpu state and return XDP_REDIRECT. The
> per-cpu state is picked up in xdp_do_redirect and xdp_flush.
>
> An approach like this would be general, and apply to all modes
> automatically.
>
> Thoughts?
All the default program does is check that the map entry contains a xsk,
and call bpf_redirect_map(). So this is pretty much the same as above,
without any special case handling.
Why would this be so expensive? Is the JIT compilation time being
counted?
--
Jonathan
>
>>>
>>> * 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.
>>
>> I tried to make this as generic as possible and make the changes to
>> the
>> driver very minimal, but could not find a way to avoid any changes at
>> all to the driver. xdp_do_direct() gets called based after the call
>> to
>> bpf_prog_run_xdp() in the 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(-)
>>>>
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