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

From: Breno Leitao <[email-masked]>
Date: Fri, 22 Mar 2024 03:21:21 -0700

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 <[email-masked]> 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