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

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Date: Fri, 22 Mar 2024 03:21:21 -0700
From: Breno Leitao <leitao@...ian.org>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: rbc@...a.com, riel@...riel.com, stable@...r.kernel.org,
	qemu-devel@...gnu.org,
	"open list:VIRTIO CORE AND NET DRIVERS" <virtualization@...ts.linux.dev>,
	"open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Andrew Melnychenko <andrew@...nix.com>
Subject: Re: [PATCH] virtio_net: Do not send RSS key if it is not supported

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@...ian.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