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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jakub Kicinski <kuba@kernel.org>,
	Jesper Dangaard Brouer <jbrouer@redhat.com>
Cc: David Ahern <dsahern@gmail.com>, David Ahern <dsahern@kernel.org>,
	netdev@vger.kernel.org, prashantbhole.linux@gmail.com,
	jasowang@redhat.com, davem@davemloft.net, mst@redhat.com,
	toshiaki.makita1@gmail.com, daniel@iogearbox.net,
	john.fastabend@gmail.com, ast@kernel.org, kafai@fb.com,
	songliubraving@fb.com, yhs@fb.com, andriin@fb.com,
	David Ahern <dahern@digitalocean.com>
Subject: Re: [PATCH bpf-next 03/12] net: Add IFLA_XDP_EGRESS for XDP programs in the egress path
Date: Sat, 01 Feb 2020 17:03:19 +0100	[thread overview]
Message-ID: <87lfpme1mg.fsf@toke.dk> (raw)
In-Reply-To: <20200130064517.43f2064f@cakuba>

Jakub Kicinski <kuba@kernel.org> writes:

> On Tue, 28 Jan 2020 15:13:43 +0100, Jesper Dangaard Brouer wrote:
>> On Sun, 26 Jan 2020 14:17:01 -0800
>> Jakub Kicinski <kuba@kernel.org> wrote:
>> 
>> > On Sun, 26 Jan 2020 13:49:33 +0100, Jesper Dangaard Brouer wrote:  
>> > > Yes, please. I want this NIC TX hook to see both SKBs and xdp_frames.    
>> > 
>> > Any pointers on what for? Unless we see actual use cases there's
>> > a justifiable concern of the entire thing just being an application of
>> > "We can solve any problem by introducing an extra level of indirection."  
>> 
>> I have two use-cases:
>> 
>> (1) For XDP easier handling of interface specific setting on egress,
>> e.g. pushing a VLAN-id, instead of having to figure this out in RX hook.
>> (I think this is also David Ahern's use-case)
>
> Is it really useful to have a hook before multi-buffer frames are
> possible and perhaps TSO? The local TCP performance is going to tank
> with XDP enabled otherwise.

For a software router (i.e., something that mostly forwards packets) it
can still be useful without multi-buffer. But yeah, that is definitely
something we need to solve, regardless of where this goes.

>> (2) I want this egress XDP hook to have the ability to signal
>> backpressure. Today we have BQL in most drivers (which is essential to
>> avoid bufferbloat). For XDP_REDIRECT we don't, which we must solve.
>> 
>> For use-case(2), we likely need a BPF-helper calling netif_tx_stop_queue(),
>> or a return code that can stop the queue towards the higher layers.
>
> Agreed, although for that use case, I'm not sure if non-XDP frames 
> have to pass trough the hook. Hard to tell as the current patches 
> don't touch on this use case.

I think it would be weird and surprising if it *doesn't* see packets
from the stack. On RX, XDP sees everything; the natural expectation
would be that this was also the case on TX, no?

-Toke


  reply	other threads:[~2020-02-01 16:03 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-23  1:41 [PATCH bpf-next 00/12] Add support for XDP in egress path David Ahern
2020-01-23  1:41 ` [PATCH bpf-next 01/12] net: Add new XDP setup and query commands David Ahern
2020-01-23  1:42 ` [PATCH bpf-next 02/12] net: Add BPF_XDP_EGRESS as a bpf_attach_type David Ahern
2020-01-23 11:34   ` Toke Høiland-Jørgensen
2020-01-23 21:32     ` David Ahern
2020-01-24  9:49       ` Toke Høiland-Jørgensen
2020-01-24  7:33   ` Martin Lau
2020-01-23  1:42 ` [PATCH bpf-next 03/12] net: Add IFLA_XDP_EGRESS for XDP programs in the egress path David Ahern
2020-01-23 11:35   ` Toke Høiland-Jørgensen
2020-01-23 21:33     ` David Ahern
2020-01-24 15:21       ` Jakub Kicinski
2020-01-24 15:36         ` Toke Høiland-Jørgensen
2020-01-26  1:43           ` David Ahern
2020-01-26  4:54             ` Alexei Starovoitov
2020-02-02 17:59               ` David Ahern
2020-01-26 12:49             ` Jesper Dangaard Brouer
2020-01-26 16:38               ` David Ahern
2020-01-26 22:17               ` Jakub Kicinski
2020-01-28 14:13                 ` Jesper Dangaard Brouer
2020-01-30 14:45                   ` Jakub Kicinski
2020-02-01 16:03                     ` Toke Høiland-Jørgensen [this message]
2020-02-02 17:48                       ` David Ahern
2020-01-26 22:11             ` Jakub Kicinski
2020-01-27  4:03               ` David Ahern
2020-01-27 14:16                 ` Jakub Kicinski
2020-01-28  3:43                   ` David Ahern
2020-01-28 13:57                     ` Jakub Kicinski
2020-02-01 16:24                       ` Toke Høiland-Jørgensen
2020-02-01 17:08                         ` Jakub Kicinski
2020-02-01 20:05                           ` Toke Høiland-Jørgensen
2020-02-02  4:15                             ` Jakub Kicinski
2020-02-03 19:56                               ` Toke Høiland-Jørgensen
2020-02-03 20:13                               ` Toke Høiland-Jørgensen
2020-02-03 22:15                                 ` Jesper Dangaard Brouer
2020-02-04 11:00                                   ` Toke Høiland-Jørgensen
2020-02-04 17:09                                     ` Jakub Kicinski
2020-02-05 15:30                                       ` Toke Høiland-Jørgensen
2020-02-02 17:45                           ` David Ahern
2020-02-02 19:12                             ` Jakub Kicinski
2020-02-02 17:43                       ` David Ahern
2020-02-02 19:31                         ` Jakub Kicinski
2020-02-02 21:51                           ` David Ahern
2020-02-01 15:59             ` Toke Høiland-Jørgensen
2020-02-02 17:54               ` David Ahern
2020-02-03 20:09                 ` Toke Høiland-Jørgensen
2020-01-23  1:42 ` [PATCH bpf-next 04/12] net: core: rename netif_receive_generic_xdp() to do_generic_xdp_core() David Ahern
2020-01-23  1:42 ` [PATCH bpf-next 05/12] tuntap: check tun_msg_ctl type at necessary places David Ahern
2020-01-23  1:42 ` [PATCH bpf-next 06/12] tun: move shared functions to if_tun.h David Ahern
2020-01-23  1:42 ` [PATCH bpf-next 07/12] vhost_net: user tap recvmsg api to access ptr ring David Ahern
2020-01-23  8:26   ` Michael S. Tsirkin
2020-01-23  1:42 ` [PATCH bpf-next 08/12] tuntap: remove usage of ptr ring in vhost_net David Ahern
2020-01-23  1:42 ` [PATCH bpf-next 09/12] tun: set egress XDP program David Ahern
2020-01-23  1:42 ` [PATCH bpf-next 10/12] tun: run XDP program in tx path David Ahern
2020-01-23  8:23   ` Michael S. Tsirkin
2020-01-24 13:36     ` Prashant Bhole
2020-01-24 13:44     ` Prashant Bhole
2020-01-23  1:42 ` [PATCH bpf-next 11/12] libbpf: Add egress XDP support David Ahern
2020-01-23  1:42 ` [PATCH bpf-next 12/12] samples/bpf: xdp1, add " David Ahern

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