@@ -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
@@ -2025,6 +2025,7 @@ static inline int ethtool_validate_duplex(__u8 duplex)
#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_SYMMETRIC (1 << 30)
#define RXH_DISCARD (1 << 31)
#define RX_CLS_FLOW_DISC 0xffffffffffffffffULL
@@ -980,6 +980,17 @@ static noinline_for_stack int ethtool_set_rxnfc(struct net_device *dev,
if (rc)
return rc;
+ /* If a symmetric hash is requested, then:
+ * 1 - no other fields besides IP src/dst and/or L4 src/dst
+ * 2 - If src is set, dst must also be set
+ */
+ if ((info.data & RXH_SYMMETRIC) &&
+ ((info.data & ~(RXH_SYMMETRIC | RXH_IP_SRC | RXH_IP_DST |
+ RXH_L4_B_0_1 | RXH_L4_B_2_3)) ||
+ (!!(info.data & RXH_IP_SRC) ^ !!(info.data & RXH_IP_DST)) ||
+ (!!(info.data & RXH_L4_B_0_1) ^ !!(info.data & RXH_L4_B_2_3))))
+ return -EINVAL;
+
rc = dev->ethtool_ops->set_rxnfc(dev, &info);
if (rc)
return rc;
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. Only fields that has counterparts in the other direction can be accepted; IP src/dst and L4 src/dst ports. 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 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@intel.com> Signed-off-by: Ahmed Zaki <ahmed.zaki@intel.com> --- Documentation/networking/scaling.rst | 6 ++++++ include/uapi/linux/ethtool.h | 1 + net/ethtool/ioctl.c | 11 +++++++++++ 3 files changed, 18 insertions(+)