Re: XDP_REDIRECT with xsks_map and dev_map

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Maciej Fijalkowski <maciej.fijalkowski@intel.com> writes:

> On Wed, Jun 03, 2020 at 12:49:25PM +0200, Toke Høiland-Jørgensen wrote:
>> maharishi bhargava <bhargavamaharishi@gmail.com> writes:
>> 
>> > On Tue, Jun 2, 2020 at 9:31 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>> >>
>> >> maharishi bhargava <bhargavamaharishi@gmail.com> writes:
>> >>
>> >> > On Tue 2 Jun, 2020, 14:31 Toke Høiland-Jørgensen, <toke@redhat.com> wrote:
>> >> >>
>> >> >> maharishi bhargava <bhargavamaharishi@gmail.com> writes:
>> >> >>
>> >> >> > Hi, in my XDP program, I want to redirect some packets using AF_XDP
>> >> >> > and redirect other packets directly from driver space.
>> >> >> > Redirection through AF_XDP works fine, but redirection through dev map
>> >> >> > stops after some packets are processed.
>> >> >>
>> >> >> Do you mean it stops even if you are *only* redirecting to a devmap, or
>> >> >> if you are first redirecting a few packets to AF_XDP, then to devmap?
>> >> >>
>> >> >> Also, which driver(s) are the physical NICs you're redirecting to/from
>> >> >> using, and which kernel version are you on?
>> >> >>
>> >> >> -Toke
>> >> >
>> >> >
>> >> >
>> >> > Currently, I'm trying to redirect packets only using devmap. But also
>> >> > have code for redirection using AF_XDP(only when a given condition is
>> >> > satisfied). A DPDK program is running in userspace which will receive
>> >> > packets from AF_XDP.
>> >>
>> >> Right, so it's just devmap redirect that breaks. What do you mean
>> >> 'redirection stops', exactly? How are you seeing this? Does xdp_monitor
>> >> (from samples/bpf) report any exceptions?
>> >>
>> >> -Toke
>> >>
>> > So, In my setup, there are three systems, Let's Assume A, B, C. System
>> > B is acting as a forwarder between A and C. So I can see the number of
>> > packets received at system C. To be specific, only 1024 packets are
>> > received. If I remove the xsks_map part from the code and don't run
>> > DPDK in userspace. This problem does not occur. Also if I forward all
>> > the packets using AF_XDP, there is no such issue.
>> 
>> I thought you said you were seeing the problem when only redirecting to
>> a devmap? So why does the xsk_map code impact this? I think you may have
>> to share some code...
>
> Isn't the case here that either xsk_map or dev_map consumes the frame and
> therefore the latter doesn't see it? so cloning might be needed here?

Yeah, certainly you can't redirect *the same packet* to both xsk_map and
devmap - but that wasn't what I understood was the use case here?

-Toke