Implementing a simple TAP PMD to dpdk-vhost structure

[Nicolson Ken (ニコルソン ケン)]

Hi Maxime,

> Maybe you could use testpmd application instead, with net_tap PMD and a net_pcap PMD?

I have an existing solution that uses the TAP PMD which I then add to a standard kernel bridge that allows me to have two-way communication with the Guest VM, but I suspect the performance would be better if we were to use a DPDK virtio-based solution; otherwise I could just drop DPDK all together and use tcpreplay, etc to directly access the bridge.

[Also net_pcap only outputs to kernel interface (or to a file or null) as it uses libpcap APIs for Tx]

> An alternative to net_tap could be to use Virtio-user PMD with Vhost- kernel backend.

That uses KNI, which the documentation says is deprecated, and I'm not sure I want to start mucking about with kernel drivers.

Thanks,
Ken

-----Original Message-----
From: Maxime Coquelin <maxime.coquelin at redhat.com> 
Sent: Wednesday, September 6, 2023 4:16 PM
To: David Marchand <david.marchand at redhat.com>; Nicolson Ken (ニコルソン ケン) <ken.nicolson at jp.panasonic.com>
Cc: users at dpdk.org; Xia, Chenbo <chenbo.xia at intel.com>
Subject: Re: Implementing a simple TAP PMD to dpdk-vhost structure



On 9/6/23 08:07, David Marchand wrote:
> Hello Ken,
> 
> On Wed, Sep 6, 2023 at 3:56 AM Nicolson Ken (ニコルソン ケン)
> <ken.nicolson at jp.panasonic.com> wrote:
>>
>> Hi all,
>>
>> Using dpdk 22.11.2 on Ubuntu 22.04
>>
>> I have a really simple use case, but I cannot find how to implement it. I've set up QEMU with all the required virtio support, so I just need to configure my Host OS-side. I want to send data from a PCAP file via tcpreplay from the Host to the Guest, so I use this command line:
>>
>> $ sudo /home/integ/dpdk-stable-22.11.2/build/examples/dpdk-vhost -l 
>> 0-3 -n 4 --socket-mem 1024 --vdev 'net_tap0' -- --socket-file 
>> /tmp/sock0 --client -p 1
>>
>> However, this fails with:
>>
>> EAL: Detected CPU lcores: 20
>> EAL: Detected NUMA nodes: 1
>> EAL: Detected static linkage of DPDK
>> EAL: Multi-process socket /var/run/dpdk/rte/mp_socket
>> EAL: Selected IOVA mode 'PA'
>> VHOST_PORT: Failed to get VMDq info.
>> EAL: Error - exiting with code: 1
>>    Cause: Cannot initialize network ports
>>
>> The offending code is from examples/vhost/main.c:
>>
>>          if (dev_info.max_vmdq_pools == 0) {
>>                  RTE_LOG(ERR, VHOST_PORT, "Failed to get VMDq info.\n");
>>                  return -1;
>>          }
>>
>> This is because the TAP PMD doesn't support VMDq pools.
>>
>> Is there an easy way to get this to work?
> 
> This sounds strange to require VMDq support...
> Copying Maxime and Chenbo who probably know better about this example code.
> 
> Alternatively, did you consider using testpmd with the vhost pmd instead ?
> 
> 

Maybe you could use testpmd application instead, with net_tap PMD and a net_pcap PMD?

An alternative to net_tap could be to use Virtio-user PMD with Vhost- kernel backend.

Maxime