Re: [PATCH] virtio_net: Do not send RSS key if it is not supported

[Breno Leitao]

Hello Xuan,

On Fri, Mar 22, 2024 at 10:00:22AM +0800, Xuan Zhuo wrote:
> On Thu, 21 Mar 2024 09:54:30 -0700, Breno Leitao <leitao@debian.org> wrote:

> > 4) Since the command above does not have a key, then the last
> >    scatter-gatter entry will be zeroed, since rss_key_size == 0.
> >     sg_buf_size = vi->rss_key_size;
> 
> 
> 
>       if (vi->has_rss || vi->has_rss_hash_report) {
>               vi->rss_indir_table_size =
>                       virtio_cread16(vdev, offsetof(struct virtio_net_config,
>                               rss_max_indirection_table_length));
>               vi->rss_key_size =
>                       virtio_cread8(vdev, offsetof(struct virtio_net_config, 
> rss_max_key_size));
> 
>               vi->rss_hash_types_supported =
>                   virtio_cread32(vdev, offsetof(struct virtio_net_config, 
> supported_hash_types));
>               vi->rss_hash_types_supported &=
>                               ~(VIRTIO_NET_RSS_HASH_TYPE_IP_EX |
>                                 VIRTIO_NET_RSS_HASH_TYPE_TCP_EX |
>                                 VIRTIO_NET_RSS_HASH_TYPE_UDP_EX);
> 
>               dev->hw_features |= NETIF_F_RXHASH;
>       }
> 
> 
> vi->rss_key_size is initiated here, I wonder if there is something wrong?

Not really, the code above is never executed (in my machines). This is
because `vi->has_rss` and `vi->has_rss_hash_report` are both unset.

Looking further, vdev does not have the VIRTIO_NET_F_RSS and
VIRTIO_NET_F_HASH_REPORT features.

Also, when I run `ethtool -x`, I got:

        # ethtool  -x eth0
        RX flow hash indirection table for eth0 with 1 RX ring(s):
        Operation not supported
        RSS hash key:
        Operation not supported
        RSS hash function:
            toeplitz: on
            xor: off
            crc32: off