linux-kernel - Re: [RFC 00/12] io

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Date:   Wed, 1 Dec 2021 15:35:49 -0700
From:   David Ahern <dsahern@...il.com>
To:     Martin KaFai Lau <kafai@...com>,
        Pavel Begunkov <asml.silence@...il.com>
Cc:     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 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.


> 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
>