Subject: Re: [PATCH 1/2] virtio-net: don't disable guest csum when disable LRO

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 28 Sep 2020 15:21:07 -0400

On Mon, Sep 28, 2020 at 11:39:14AM +0800, [email-masked] wrote:
> From: Tonghao Zhang <[email-masked]>
> 
> Open vSwitch and Linux bridge will disable LRO of the interface
> when this interface added to them. Now when disable the LRO, the
> virtio-net csum is disable too. That drops the forwarding performance.
> 
> Fixes: e59ff2c49ae1 ("virtio-net: disable guest csum during XDP set")

I am a bit confused by this tag. Did this change bring about
disabling checksum when LRO is disabled? I am not sure
I follow how ...

> Cc: Michael S. Tsirkin <[email-masked]>
> Cc: Jason Wang <[email-masked]>
> Cc: Willem de Bruijn <[email-masked]>
> Signed-off-by: Tonghao Zhang <[email-masked]>
> ---
>  drivers/net/virtio_net.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7145c83c6c8c..21b71148c532 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -63,6 +63,11 @@ static const unsigned long guest_offloads[] = {
>  	VIRTIO_NET_F_GUEST_CSUM
>  };
>  
> +#define GUEST_OFFLOAD_LRO_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
> +				(1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
> +				(1ULL << VIRTIO_NET_F_GUEST_ECN)  | \
> +				(1ULL << VIRTIO_NET_F_GUEST_UFO))
> +
>  struct virtnet_stat_desc {
>  	char desc[ETH_GSTRING_LEN];
>  	size_t offset;
> @@ -2531,7 +2536,8 @@ static int virtnet_set_features(struct net_device *dev,
>  		if (features & NETIF_F_LRO)
>  			offloads = vi->guest_offloads_capable;
>  		else
> -			offloads = 0;
> +			offloads = vi->guest_offloads_capable &
> +				   ~GUEST_OFFLOAD_LRO_MASK;
>  
>  		err = virtnet_set_guest_offloads(vi, offloads);
>  		if (err)
> -- 
> 2.23.0