netdev - Re: [PATCH v6 1/6] virtio_net: Add functions for hashing

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Message-ID: <677fd98d89df1_362bc12942f@willemb.c.googlers.com.notmuch>
Date: Thu, 09 Jan 2025 09:13:33 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Akihiko Odaki <akihiko.odaki@...nix.com>, 
 Jonathan Corbet <corbet@....net>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.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>, 
 "Michael S. Tsirkin" <mst@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
 Shuah Khan <shuah@...nel.org>, 
 linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 netdev@...r.kernel.org, 
 kvm@...r.kernel.org, 
 virtualization@...ts.linux-foundation.org, 
 linux-kselftest@...r.kernel.org, 
 Yuri Benditovich <yuri.benditovich@...nix.com>, 
 Andrew Melnychenko <andrew@...nix.com>, 
 Stephen Hemminger <stephen@...workplumber.org>, 
 gur.stavi@...wei.com, 
 Akihiko Odaki <akihiko.odaki@...nix.com>
Subject: Re: [PATCH v6 1/6] virtio_net: Add functions for hashing

Akihiko Odaki wrote:
> They are useful to implement VIRTIO_NET_F_RSS and
> VIRTIO_NET_F_HASH_REPORT.

Toeplitz potentially has users beyond virtio. I wonder if we should
from the start implement this as net/core/rss.c.

> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>  include/linux/virtio_net.h | 188 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 188 insertions(+)
> 
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index 02a9f4dc594d..3b25ca75710b 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -9,6 +9,194 @@
>  #include <uapi/linux/tcp.h>
>  #include <uapi/linux/virtio_net.h>
>  
> +struct virtio_net_hash {
> +	u32 value;
> +	u16 report;
> +};
> +
> +struct virtio_net_toeplitz_state {
> +	u32 hash;
> +	const u32 *key;
> +};
> +
> +#define VIRTIO_NET_SUPPORTED_HASH_TYPES (VIRTIO_NET_RSS_HASH_TYPE_IPv4 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_TCPv4 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_IPv6 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_TCPv6 | \
> +					 VIRTIO_NET_RSS_HASH_TYPE_UDPv6)
> +
> +#define VIRTIO_NET_RSS_MAX_KEY_SIZE 40
> +
> +static inline void virtio_net_toeplitz_convert_key(u32 *input, size_t len)
> +{
> +	while (len >= sizeof(*input)) {
> +		*input = be32_to_cpu((__force __be32)*input);
> +		input++;
> +		len -= sizeof(*input);
> +	}
> +}
> +
> +static inline void virtio_net_toeplitz_calc(struct virtio_net_toeplitz_state *state,
> +					    const __be32 *input, size_t len)
> +{
> +	while (len >= sizeof(*input)) {
> +		for (u32 map = be32_to_cpu(*input); map; map &= (map - 1)) {
> +			u32 i = ffs(map);
> +
> +			state->hash ^= state->key[0] << (32 - i) |
> +				       (u32)((u64)state->key[1] >> i);
> +		}
> +
> +		state->key++;
> +		input++;
> +		len -= sizeof(*input);
> +	}
> +}

Have you verified that this algorithm matches a known toeplitz
implementation. And computes the expected values for the test
inputs in

https://learn.microsoft.com/en-us/windows-hardware/drivers/network/verifying-the-rss-hash-calculation

We have a toeplitz implementation in
tools/testing/selftests/net/toeplitz.c that can also be used as
reference.

> +
> +static inline u8 virtio_net_hash_key_length(u32 types)
> +{
> +	size_t len = 0;
> +
> +	if (types & VIRTIO_NET_HASH_REPORT_IPv4)
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv4_addrs));
> +
> +	if (types &
> +	    (VIRTIO_NET_HASH_REPORT_TCPv4 | VIRTIO_NET_HASH_REPORT_UDPv4))
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv4_addrs) +
> +			  sizeof(struct flow_dissector_key_ports));
> +
> +	if (types & VIRTIO_NET_HASH_REPORT_IPv6)
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv6_addrs));
> +
> +	if (types &
> +	    (VIRTIO_NET_HASH_REPORT_TCPv6 | VIRTIO_NET_HASH_REPORT_UDPv6))
> +		len = max(len,
> +			  sizeof(struct flow_dissector_key_ipv6_addrs) +
> +			  sizeof(struct flow_dissector_key_ports));
> +
> +	return len + 4;

Avoid magic constants. Please use sizeof or something else to signal
what this 4 derives from.