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

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Message-ID: <CACGkMEsKSUs77biUTF14vENM+AfrLUOHMVe4nitd9CQ-obXuCA@mail.gmail.com>
Date: Tue, 27 Aug 2024 10:03:59 +0800
From: Jason Wang <jasowang@...hat.com>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: Andrew Lunn <andrew@...n.ch>, Carlos Bilbao <cbilbao@...italocean.com>, mst@...hat.com, 
	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 Tue, Aug 27, 2024 at 12:11 AM Dragos Tatulea <dtatulea@...dia.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.

Thanks


>
> Thanks,
> Dragos
>