On 27.08.24 04:03, Jason Wang wrote:
> On Tue, Aug 27, 2024 at 12:11 AM Dragos Tatulea <dtatu...@nvidia.com> wrote:
>>
>>
>> On 26.08.24 16:24, Andrew Lunn wrote:
>>> On Mon, Aug 26, 2024 at 11:06:09AM +0200, 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.
>>>
>>> Then it should probably report DUPLEX_UNKNOWN.
>>>
>>> The speed of 0 also suggests SPEED_UNKNOWN is not being returned. So
>>> this just looks buggy in general.
>>>
>> The virtio spec doesn't mention what those values should be when
>> VIRTIO_NET_F_SPEED_DUPLEX is not supported.
>>
>> Jason, should vdpa_dev_net_config_fill() initialize the speed/duplex
>> fields to SPEED/DUPLEX_UNKNOWN instead of 0?
>
> Spec said
>
> """
> The following two fields, speed and duplex, only exist if
> VIRTIO_NET_F_SPEED_DUPLEX is set.
> """
>
> So my understanding is that it is undefined behaviour, and those
> fields seems useless before feature negotiation. For safety, it might
> be better to initialize them as UNKOWN.
>
After a closer look my statement doesn't make sense: the device will copy
the virtio_net_config bytes on top.
The solution is to initialize these fields to UNKNOWN in the driver. Will send
a patch to fix this.
Thanks,
Dragos
