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

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Message-ID: <8a15a46a-2744-4474-8add-7f6fb35552b3@digitalocean.com>
Date: Mon, 26 Aug 2024 09:26:25 -0500
From: Carlos Bilbao <cbilbao@...italocean.com>
To: Dragos Tatulea <dtatulea@...dia.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?

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.

>
>> 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?

>
> Thanks,
> Dragos

Thank you!
Carlos