netdev - Re: [RFC 00/12] io_uring zerocopy send

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Message-ID: <20211201230757.fuhnhgtbx5o22wgs@kafai-mbp.dhcp.thefacebook.com>
Date:   Wed, 1 Dec 2021 15:07:57 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     David Ahern <dsahern@...il.com>
CC:     Pavel Begunkov <asml.silence@...il.com>,
        <io-uring@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Jakub Kicinski <kuba@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [RFC 00/12] io_uring zerocopy send

On Wed, Dec 01, 2021 at 03:35:49PM -0700, David Ahern wrote:
> On 12/1/21 2:51 PM, Martin KaFai Lau wrote:
> > 
> > To tx out dummy, I did:
> > #> ip a add 10.0.0.1/24 dev dummy0
>               ^^^^^^^^
> > 
> > #> ip -4 r
> > 10.0.0.0/24 dev dummy0 proto kernel scope link src 10.0.0.1
> > 
> > #> ./send-zc -4 -D 10.0.0.(2) -t 10 udp
>                      ^^^^^^^^^^
> 
> Pavel's commands have: 'send-zc -4 -D <dummy_ip_addr> -t 10 udp'
> 
> I read dummy_ip_addr as the address assigned to dummy0; that's an
> important detail. You are sending to an address on that network, not the
> address assigned to the device, in which case packets are created and
> then dropped by the dummy driver - nothing actually makes it to the server.
Right, I assumed "dropped by dummy driver" is the usual intention
for using dummy, so just in case if it was the intention for
testing tx only.  You are right and it seems the intention
of this command is to have server receiving the packets.

> 
> 
> > ip -s link show dev dummy0
> > 2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 65535 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
> >    link/ether 82:0f:e0:dc:f7:e6 brd ff:ff:ff:ff:ff:ff
> >    RX:    bytes packets errors dropped  missed   mcast
> >               0       0      0       0       0       0
> >    TX:    bytes packets errors dropped carrier collsns
> >    140800890299 2150397      0       0       0       0
> > 
>