netdev - Re: [PATCH bpf-next] xsk: support AF

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Message-ID: <20210528093213.GB46923@ranger.igk.intel.com>
Date:   Fri, 28 May 2021 11:32:13 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Xie He <xie.he.0141@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        John Ogness <john.ogness@...utronix.de>,
        Wang Hai <wanghai38@...wei.com>,
        Tanner Love <tannerlove@...gle.com>,
        Eyal Birger <eyal.birger@...il.com>,
        Menglong Dong <dong.menglong@....com.cn>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next] xsk: support AF_PACKET

On Fri, May 28, 2021 at 11:25:56AM +0200, Toke Høiland-Jørgensen wrote:
> Xuan Zhuo <xuanzhuo@...ux.alibaba.com> writes:
> 
> > On Fri, 28 May 2021 10:55:58 +0200, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> >> Xuan Zhuo <xuanzhuo@...ux.alibaba.com> writes:
> >>
> >> > In xsk mode, users cannot use AF_PACKET(tcpdump) to observe the current
> >> > rx/tx data packets. This feature is very important in many cases. So
> >> > this patch allows AF_PACKET to obtain xsk packages.
> >>
> >> You can use xdpdump to dump the packets from the XDP program before it
> >> gets redirected into the XSK:
> >> https://github.com/xdp-project/xdp-tools/tree/master/xdp-dump
> >
> > Wow, this is a good idea.
> >
> >>
> >> Doens't currently work on egress, but if/when we get a proper TX hook
> >> that should be doable as well.
> >>
> >> Wiring up XSK to AF_PACKET sounds a bit nonsensical: XSK is already a
> >> transport to userspace, why would you need a second one?
> >
> > I have some different ideas. In my opinion, just like AF_PACKET can monitor
> > tcp/udp packets, AF_PACKET monitors xsk packets is the same.
> 
> But you're adding code in the fast path to do this, in a code path where
> others have been working quite hard to squeeze out every drop of
> performance (literally chasing single nanoseconds). So I'm sorry, but
> this approach is just not going to fly.

+1. Probably would be better for everyone if Xuan started a thread on list
what is his need.

> 
> What is your use case anyway? Yes, being able to run tcpdump and see the
> packets is nice and convenient, but what do you actually want to use
> this for? Just for debugging your application? System monitoring?
> Something else?
> 
> -Toke
>