Re: [RFC 00/12] io_uring zerocopy send

On 12/1/21 23:07, Martin KaFai Lau wrote:

On Wed, Dec 01, 2021 at 03:35:49PM -0700, David Ahern wrote:

quoted

On 12/1/21 2:51 PM, Martin KaFai Lau wrote:

quoted

To tx out dummy, I did:
#> ip a add 10.0.0.1/24 dev dummy0

               ^^^^^^^^

quoted

#> 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.

I see, it seems we found the misunderstanding:

For dummy device, I indeed was testing only tx part without
a server, in my understanding it better approximates an actual
fast NIC. I don't think dummy is even capable to pass the data,
so was thinking that it's given that there is no receive side,
and so no "msg_zerocopy -r".

For localhost testing (with the hack), there was a server
verifying data.

quoted

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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

-- 
Pavel Begunkov