Re: [PATCH 1/2] vdpa/mlx5: Make VIRTIO_NET_F_MRG_RXBUF off by default

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Eli Cohen <elic@nvidia.com>
Cc: perezma@redhat.com, parav@mellanox.com,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 1/2] vdpa/mlx5: Make VIRTIO_NET_F_MRG_RXBUF off by default
Date: Sun, 12 Mar 2023 04:58:07 -0400	[thread overview]
Message-ID: <20230312045717-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20230312083920.2300028-2-elic@nvidia.com>

On Sun, Mar 12, 2023 at 10:39:19AM +0200, Eli Cohen wrote:
> One can still enable it when creating the vdpa device using vdpa tool by
> providing features that include it.
> 
> For example:
> $ vdpa dev add name vdpa0 mgmtdev pci/0000:86:00.2 device_features 0x300cb982b
> 
> Signed-off-by: Eli Cohen <elic@nvidia.com>

What's the reason to turn it off by default? It's generally a
performance win isn't it?

> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 4abc3a4ee515..3858ba1e8975 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -3154,6 +3154,8 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
>  			return -EINVAL;
>  		}
>  		device_features &= add_config->device_features;
> +	} else {
> +		device_features &= ~BIT_ULL(VIRTIO_NET_F_MRG_RXBUF);
>  	}
>  	if (!(device_features & BIT_ULL(VIRTIO_F_VERSION_1) &&
>  	      device_features & BIT_ULL(VIRTIO_F_ACCESS_PLATFORM))) {
> -- 
> 2.38.1

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization