linux-kernel - Re: [RFC] Why is set_config not supported in mlx5

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Message-ID: <afcbf041-7613-48e6-8088-9d52edd907ff@nvidia.com>
Date: Mon, 26 Aug 2024 11:06:09 +0200
From: Dragos Tatulea <dtatulea@...dia.com>
To: Carlos Bilbao <cbilbao@...italocean.com>, eli@...lanox.com,
 mst@...hat.com, jasowang@...hat.com, xuanzhuo@...ux.alibaba.com
Cc: virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, kvm@...r.kernel.org, eperezma@...hat.com,
 sashal@...nel.org, yuehaibing@...wei.com, steven.sistare@...cle.com
Subject: Re: [RFC] Why is set_config not supported in mlx5_vnet?



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.


> 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`.

Thanks,
Dragos