Re: [RFC 00/12] io_uring zerocopy send

[Pavel Begunkov]

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

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.


> > > 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