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

[Carlos Bilbao <cbilbao@digitalocean.com>]

Hello,

On 8/26/24 9:07 PM, Jason Wang wrote:
> On Tue, Aug 27, 2024 at 3:23 AM Carlos Bilbao <cbilbao@digitalocean.com> wrote:
>> Hello,
>>
>> On 8/26/24 10:53 AM, Dragos Tatulea wrote:
>>> 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?
>>
>> Yes, CTRL_VQ also shows up in vdpa dev config show. There isn't a specific
>> value I want to configure ATM, but my vDPA isn't performing as expected, so
>> I'm investigating potential issues. Below is the code I used to retrieve
>> the configuration from the driver; I'd be happy to send it as a patch if
>> you or someone else reviews it.
>>
>>
>>> Thanks,
>>> Dragos
>>
>> Thanks,
>> Carlos
>>
>> ---
>>
>> From ab6ea66c926eaf1e95eb5d73bc23183e0021ee27 Mon Sep 17 00:00:00 2001
>> From: Carlos Bilbao <bilbao@vt.edu>
>> Date: Sat, 24 Aug 2024 00:24:56 +0000
>> Subject: [PATCH] mlx5: Add support to update the vDPA configuration
>>
>> This is needed for VHOST_VDPA_SET_CONFIG.
>>
>> Signed-off-by: Carlos Bilbao <cbilbao@digitalocean.com>
>> ---
>>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 22 ++++++++++++++++++++--
>>  1 file changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> index b56aae3f7be3..da31c743b2b9 100644
>> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
>> @@ -2909,14 +2909,32 @@ static void mlx5_vdpa_get_config(struct vdpa_device *vdev, unsigned int offset,
>>      struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>>      struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
>>
>> -    if (offset + len <= sizeof(struct virtio_net_config))
>> +    if (offset + len <= sizeof(struct virtio_net_config)) {
>>          memcpy(buf, (u8 *)&ndev->config + offset, len);
>> +        }
>> +        else
>> +        {
>> +            printk(KERN_ERR "%s: Offset and length out of bounds\n",
>> +            __func__);
>> +        }
>> +
>>  }
>>
>>  static void mlx5_vdpa_set_config(struct vdpa_device *vdev, unsigned int offset, const void *buf,
>>                   unsigned int len)
>>  {
>> -    /* not supported */
>> +    struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>> +    struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
>> +
>> +    if (offset + len <= sizeof(struct virtio_net_config))
>> +    {
>> +        memcpy((u8 *)&ndev->config + offset, buf, len);
>> +    }
>> +    else
>> +    {
>> +        printk(KERN_ERR "%s: Offset and length out of bounds\n",
>> +        __func__);
>> +    }
>>  }
> This should follow the virtio-spec, for modern virtio-net devices,
> most of the fields are read only.


Ack, according to:

https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html

I believe only duplex and speed can be changed. Will resend patch.


> Thanks
>
>>  static u32 mlx5_vdpa_get_generation(struct vdpa_device *vdev)
>> --
>> 2.34.1
>>
>>

Thanks,
Carlos