netdev - Re: [PATCH bpf-next v4 00/17] AF_XDP infrastructure improvements and mlx5e support

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Message-ID: <CAJ+HfNiXbPUh2zhMJN9=O2a_8nBak2yOeVvZNJaofY4S624N+w@mail.gmail.com>
Date:   Thu, 13 Jun 2019 16:53:47 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jonathan Lemon <bsd@...com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Maciej Fijalkowski <maciejromanfijalkowski@...il.com>
Subject: Re: [PATCH bpf-next v4 00/17] AF_XDP infrastructure improvements and
 mlx5e support

On Thu, 13 Jun 2019 at 16:11, Björn Töpel <bjorn.topel@...el.com> wrote:
>
>
> On 2019-06-13 16:01, Maxim Mikityanskiy wrote:
> > On 2019-06-13 15:58, Björn Töpel wrote:
> >> On Wed, 12 Jun 2019 at 22:49, Jakub Kicinski
> >> <jakub.kicinski@...ronome.com> wrote:
> >>>
> >>> On Wed, 12 Jun 2019 15:56:33 +0000, Maxim Mikityanskiy wrote:
> >>>> UAPI is not changed, XSK RX queues are exposed to the kernel. The lower
> >>>> half of the available amount of RX queues are regular queues, and the
> >>>> upper half are XSK RX queues.
> >>>
> >>> If I have 32 queues enabled on the NIC and I install AF_XDP socket on
> >>> queue 10, does the NIC now have 64 RQs, but only first 32 are in the
> >>> normal RSS map?
> >>>
> >>
> >> Additional, related, question to Jakub's: Say that I'd like to hijack
> >> all 32 Rx queues of the NIC. I create 32 AF_XDP socket and attach them
> >> in zero-copy mode to the device. What's the result?
> >
> > There are 32 regular RX queues (0..31) and 32 XSK RX queues (32..63). If
> > you want 32 zero-copy AF_XDP sockets, you can attach them to queues
> > 32..63, and the regular traffic won't be affected at all.
> >
> Thanks for getting back! More questions!
>
> Ok, so I cannot (with zero-copy) get the regular traffic into AF_XDP
> sockets?
>
> How does qids map? Can I only bind a zero-copy socket to qid 32..63 in
> the example above?
>
> Say that I have a a copy-mode AF_XDP socket bound to queue 2. In this
> case I will receive the regular traffic from queue 2. Enabling zero-copy
> for the same queue, will this give an error, or receive AF_XDP specific
> traffic from queue 2+32? Or return an error, and require an explicit
> bind to any of the queues 32..63?
>
>

Let me expand a bit on why I'm asking these qid questions.

It's unfortunate that vendors have different view/mapping on
"qids". For Intel, we allow to bind a zero-copy socket to all Rx
qids. For Mellanox, a certain set of qids are allowed for zero-copy
sockets.

This highlights a need for a better abstraction for queues than "some
queue id from ethtool". This will take some time, and I think that we
have to accept for now that we'll have different behavior/mapping for
zero-copy sockets on different NICs.

Let's address this need for a better queue abstraction, but that
shouldn't block this series IMO. Other than patch:

"[PATCH bpf-next v4 07/17] libbpf: Support drivers with non-combined channels"

which I'd like to see a bit more discussion on, I'm OK with this
series. I haven't been able to test it (no hardware "hint, hint"), but
I know Jonathan has been running it.

Thanks for working on this, Max!

Björn