Re: [RFC] Why is set_config not supported in mlx5_vnet?

[Dragos Tatulea <dtatulea@nvidia.com>]

On 26.08.24 16:26, Carlos Bilbao wrote:
> Hello Dragos,
> 
> On 8/26/24 4:06 AM, Dragos Tatulea wrote:
>>
>> On 23.08.24 18:54, Carlos Bilbao wrote:
>>> Hello,
>>>
>>> I'm debugging my vDPA setup, and when using ioctl to retrieve the
>>> configuration, I noticed that it's running in half duplex mode:
>>>
>>> Configuration data (24 bytes):
>>>   MAC address: (Mac address)
>>>   Status: 0x0001
>>>   Max virtqueue pairs: 8
>>>   MTU: 1500
>>>   Speed: 0 Mb
>>>   Duplex: Half Duplex
>>>   RSS max key size: 0
>>>   RSS max indirection table length: 0
>>>   Supported hash types: 0x00000000
>>>
>>> I believe this might be contributing to the underperformance of vDPA.
>> mlx5_vdpa vDPA devicess currently do not support the VIRTIO_NET_F_SPEED_DUPLEX
>> feature which reports speed and duplex. You can check the state on the
>> PF.
> 
> 
> According to ethtool, all my devices are running at full duplex. I assume I
> can disregard this configuration output from the module then.
> 
Yep.

> 
>>
>>> While looking into how to change this option for Mellanox, I read the following
>>> kernel code in mlx5_vnet.c:
>>>
>>> static void mlx5_vdpa_set_config(struct vdpa_device *vdev, unsigned int offset, const void *buf,
>>>                  unsigned int len)
>>> {
>>>     /* not supported */
>>> }
>>>
>>> I was wondering why this is the case.
>> TBH, I don't know why it was not added. But in general, the control VQ is the
>> better way as it's dynamic.
>>
>>> Is there another way for me to change
>>> these configuration settings?
>>>
>> The configuration is done using control VQ for most things (MTU, MAC, VQs,
>> etc). Make sure that you have the CTRL_VQ feature set (should be on by
>> default). It should appear in `vdpa mgmtdev show` and `vdpa dev config
>> show`.
> 
> 
> I see that CTRL_VQ is indeed enabled. Is there any documentation on how to
> use the control VQ to get/set vDPA configuration values?
> 
>
You are most likely using it already through through qemu. You can check
if the CTR_VQ feature also shows up in the output of `vdpa dev config show`.

What values are you trying to configure btw?

Thanks,
Dragos