Re: [PATCH v4 1/2] vdpa/mlx5: Make VIRTIO_NET_F_MRG_RXBUF off by default

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On Tue, Mar 21, 2023 at 01:28:08PM +0200, Eli Cohen wrote:
> Following patch adds driver support for VIRTIO_NET_F_MRG_RXBUF.
> 
> Current firmware versions show degradation in packet rate when using
> MRG_RXBUF. Users who favor memory saving over packet rate could enable
> this feature but we want to keep it off by default.
> 
> 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
> 
> 
> Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>


I have a question. Could you guys try with the recent XDP mergeable
buffer rework? Does this address the performance issue you are
observing?

Specifically:

Message-Id: <20230322025701.2955-1-xuanzhuo@xxxxxxxxxxxxxxxxx>
Message-Id: <20230322030308.16046-1-xuanzhuo@xxxxxxxxxxxxxxxxx>

I would very much appreciate if you posted perf numbers
in response to that thread - both to help evaluate that
patchset and this one.
Thanks!

> ---
>  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 520646ae7fa0..502c482a93ce 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -3122,6 +3122,8 @@ 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

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