netdev - [PATCH net-next v5 1/6] net: ethtool: allow symmetric-xor RSS hash for any flow type

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Date: Wed, 18 Oct 2023 11:06:30 -0600
From: Ahmed Zaki <ahmed.zaki@...el.com>
To: netdev@...r.kernel.org
Cc: intel-wired-lan@...ts.osuosl.org,
	corbet@....net,
	jesse.brandeburg@...el.com,
	anthony.l.nguyen@...el.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	vladimir.oltean@....com,
	andrew@...n.ch,
	horms@...nel.org,
	mkubecek@...e.cz,
	willemdebruijn.kernel@...il.com,
	linux-doc@...r.kernel.org,
	Ahmed Zaki <ahmed.zaki@...el.com>,
	Wojciech Drewek <wojciech.drewek@...el.com>
Subject: [PATCH net-next v5 1/6] net: ethtool: allow symmetric-xor RSS hash for any flow type

Symmetric RSS hash functions are beneficial in applications that monitor
both Tx and Rx packets of the same flow (IDS, software firewalls, ..etc).
Getting all traffic of the same flow on the same RX queue results in
higher CPU cache efficiency.

A NIC that supports "symmetric-xor" can achieve this RSS hash symmetry
by XORing the source and destination fields and pass the values to the
RSS hash algorithm.

The user may request RSS hash symmetry for a specific flow type, via:

    # ethtool -N|-U eth0 rx-flow-hash <flow_type> s|d|f|n symmetric-xor

or turn symmetry off (asymmetric) by:

    # ethtool -N|-U eth0 rx-flow-hash <flow_type> s|d|f|n

Reviewed-by: Wojciech Drewek <wojciech.drewek@...el.com>
Signed-off-by: Ahmed Zaki <ahmed.zaki@...el.com>
---
 Documentation/networking/scaling.rst |  6 ++++++
 include/uapi/linux/ethtool.h         | 21 +++++++++++++--------
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/Documentation/networking/scaling.rst b/Documentation/networking/scaling.rst
index 92c9fb46d6a2..64f3d7566407 100644
--- a/Documentation/networking/scaling.rst
+++ b/Documentation/networking/scaling.rst
@@ -44,6 +44,12 @@ by masking out the low order seven bits of the computed hash for the
 packet (usually a Toeplitz hash), taking this number as a key into the
 indirection table and reading the corresponding value.
 
+Some NICs support symmetric RSS hashing where, if the IP (source address,
+destination address) and TCP/UDP (source port, destination port) tuples
+are swapped, the computed hash is the same. This is beneficial in some
+applications that monitor TCP/IP flows (IDS, firewalls, ...etc) and need
+both directions of the flow to land on the same Rx queue (and CPU).
+
 Some advanced NICs allow steering packets to queues based on
 programmable filters. For example, webserver bound TCP port 80 packets
 can be directed to their own receive queue. Such “n-tuple” filters can
diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
index f7fba0dc87e5..4e8d38fb55ce 100644
--- a/include/uapi/linux/ethtool.h
+++ b/include/uapi/linux/ethtool.h
@@ -2018,14 +2018,19 @@ static inline int ethtool_validate_duplex(__u8 duplex)
 #define	FLOW_RSS	0x20000000
 
 /* L3-L4 network traffic flow hash options */
-#define	RXH_L2DA	(1 << 1)
-#define	RXH_VLAN	(1 << 2)
-#define	RXH_L3_PROTO	(1 << 3)
-#define	RXH_IP_SRC	(1 << 4)
-#define	RXH_IP_DST	(1 << 5)
-#define	RXH_L4_B_0_1	(1 << 6) /* src port in case of TCP/UDP/SCTP */
-#define	RXH_L4_B_2_3	(1 << 7) /* dst port in case of TCP/UDP/SCTP */
-#define	RXH_DISCARD	(1 << 31)
+#define	RXH_L2DA		(1 << 1)
+#define	RXH_VLAN		(1 << 2)
+#define	RXH_L3_PROTO		(1 << 3)
+#define	RXH_IP_SRC		(1 << 4)
+#define	RXH_IP_DST		(1 << 5)
+#define	RXH_L4_B_0_1		(1 << 6) /* src port in case of TCP/UDP/SCTP */
+#define	RXH_L4_B_2_3		(1 << 7) /* dst port in case of TCP/UDP/SCTP */
+/* XOR the corresponding source and destination fields of each specified
+ * protocol. Both copies of the XOR'ed fields are fed into the RSS and RXHASH
+ * calculation.
+ */
+#define	RXH_SYMMETRIC_XOR	(1 << 30)
+#define	RXH_DISCARD		(1 << 31)
 
 #define	RX_CLS_FLOW_DISC	0xffffffffffffffffULL
 #define RX_CLS_FLOW_WAKE	0xfffffffffffffffeULL
-- 
2.34.1