[PATCH bpf-next V2 1/5] igc: enable and fix RX hash usage by netstack

Jesper Dangaard Brouer
2023-04-18T13:31:42Z

When function igc_rx_hash() was introduced in v4.20 via commit 0507ef8a0372
("igc: Add transmit and receive fastpath and interrupt handlers"), the
hardware wasn't configured to provide RSS hash, thus it made sense to not
enable net_device NETIF_F_RXHASH feature bit.

The NIC hardware was configured to enable RSS hash info in v5.2 via commit
2121c2712f82 ("igc: Add multiple receive queues control supporting"), but
forgot to set the NETIF_F_RXHASH feature bit.

The original implementation of igc_rx_hash() didn't extract the associated
pkt_hash_type, but statically set PKT_HASH_TYPE_L3. The largest portions of
this patch are about extracting the RSS Type from the hardware and mapping
this to enum pkt_hash_types. This was based on Foxville i225 software user
manual rev-1.3.1 and tested on Intel Ethernet Controller I225-LM (rev 03).

For UDP it's worth noting that RSS (type) hashing have been disabled both for
IPv4 and IPv6 (see IGC_MRQC_RSS_FIELD_IPV4_UDP + IGC_MRQC_RSS_FIELD_IPV6_UDP)
because hardware RSS doesn't handle fragmented pkts well when enabled (can
cause out-of-order). This results in PKT_HASH_TYPE_L3 for UDP packets, and
hash value doesn't include UDP port numbers. Not being PKT_HASH_TYPE_L4, have
the effect that netstack will do a software based hash calc calling into
flow_dissect, but only when code calls skb_get_hash(), which doesn't
necessary happen for local delivery.

For QA verification testing I wrote a small bpftrace prog:
[0] https://github.com/xdp-project/xdp-project/blob/master/areas/hints/monitor_skb_hash_on_dev.bt

Fixes: 2121c2712f82 ("igc: Add multiple receive queues control supporting")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
drivers/net/ethernet/intel/igc/igc.h | 28 ++++++++++++++++++++++++++
drivers/net/ethernet/intel/igc/igc_main.c | 31 +++++++++++++++++++++++++----
2 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
index 34aebf00a512..f7f9e217e7b4 100644
--- a/drivers/net/ethernet/intel/igc/igc.h
+++ b/drivers/net/ethernet/intel/igc/igc.h
@@ -13,6 +13,7 @@
#include <linux/ptp_clock_kernel.h>
#include <linux/timecounter.h>
#include <linux/net_tstamp.h>
+#include <linux/bitfield.h>

#include "igc_hw.h"

@@ -311,6 +312,33 @@ extern char igc_driver_name[];
#define IGC_MRQC_RSS_FIELD_IPV4_UDP 0x00400000
#define IGC_MRQC_RSS_FIELD_IPV6_UDP 0x00800000

+/* RX-desc Write-Back format RSS Type's */
+enum igc_rss_type_num {
+ IGC_RSS_TYPE_NO_HASH = 0,
+ IGC_RSS_TYPE_HASH_TCP_IPV4 = 1,
+ IGC_RSS_TYPE_HASH_IPV4 = 2,
+ IGC_RSS_TYPE_HASH_TCP_IPV6 = 3,
+ IGC_RSS_TYPE_HASH_IPV6_EX = 4,
+ IGC_RSS_TYPE_HASH_IPV6 = 5,
+ IGC_RSS_TYPE_HASH_TCP_IPV6_EX = 6,
+ IGC_RSS_TYPE_HASH_UDP_IPV4 = 7,
+ IGC_RSS_TYPE_HASH_UDP_IPV6 = 8,
+ IGC_RSS_TYPE_HASH_UDP_IPV6_EX = 9,
+ IGC_RSS_TYPE_MAX = 10,
+};
+#define IGC_RSS_TYPE_MAX_TABLE 16
+#define IGC_RSS_TYPE_MASK GENMASK(3,0) /* 4-bits (3:0) = mask 0x0F */
+
+/* igc_rss_type - Rx descriptor RSS type field */
+static inline u32 igc_rss_type(const union igc_adv_rx_desc *rx_desc)
+{
+ /* RSS Type 4-bits (3:0) number: 0-9 (above 9 is reserved)
+ * Accessing the same bits via u16 (wb.lower.lo_dword.hs_rss.pkt_info)
+ * is slightly slower than via u32 (wb.lower.lo_dword.data)
+ */
+ return le32_get_bits(rx_desc->wb.lower.lo_dword.data, IGC_RSS_TYPE_MASK);
+}
+
/* Interrupt defines */
#define IGC_START_ITR 648 /* ~6000 ints/sec */
#define IGC_4K_ITR 980
diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 1c4676882082..bfa9768d447f 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -1690,14 +1690,36 @@ static void igc_rx_checksum(struct igc_ring *ring,
le32_to_cpu(rx_desc->wb.upper.status_error));
}

+/* Mapping HW RSS Type to enum pkt_hash_types */
+static const enum pkt_hash_types igc_rss_type_table[IGC_RSS_TYPE_MAX_TABLE] = {
+ [IGC_RSS_TYPE_NO_HASH] = PKT_HASH_TYPE_L2,
+ [IGC_RSS_TYPE_HASH_TCP_IPV4] = PKT_HASH_TYPE_L4,
+ [IGC_RSS_TYPE_HASH_IPV4] = PKT_HASH_TYPE_L3,
+ [IGC_RSS_TYPE_HASH_TCP_IPV6] = PKT_HASH_TYPE_L4,
+ [IGC_RSS_TYPE_HASH_IPV6_EX] = PKT_HASH_TYPE_L3,
+ [IGC_RSS_TYPE_HASH_IPV6] = PKT_HASH_TYPE_L3,
+ [IGC_RSS_TYPE_HASH_TCP_IPV6_EX] = PKT_HASH_TYPE_L4,
+ [IGC_RSS_TYPE_HASH_UDP_IPV4] = PKT_HASH_TYPE_L4,
+ [IGC_RSS_TYPE_HASH_UDP_IPV6] = PKT_HASH_TYPE_L4,
+ [IGC_RSS_TYPE_HASH_UDP_IPV6_EX] = PKT_HASH_TYPE_L4,
+ [10] = PKT_HASH_TYPE_NONE, /* RSS Type above 9 "Reserved" by HW */
+ [11] = PKT_HASH_TYPE_NONE, /* keep array sized for SW bit-mask */
+ [12] = PKT_HASH_TYPE_NONE, /* to handle future HW revisons */
+ [13] = PKT_HASH_TYPE_NONE,
+ [14] = PKT_HASH_TYPE_NONE,
+ [15] = PKT_HASH_TYPE_NONE,
+};
+
static inline void igc_rx_hash(struct igc_ring *ring,
union igc_adv_rx_desc *rx_desc,
struct sk_buff *skb)
{
- if (ring->netdev->features & NETIF_F_RXHASH)
- skb_set_hash(skb,
- le32_to_cpu(rx_desc->wb.lower.hi_dword.rss),
- PKT_HASH_TYPE_L3);
+ if (ring->netdev->features & NETIF_F_RXHASH) {
+ u32 rss_hash = le32_to_cpu(rx_desc->wb.lower.hi_dword.rss);
+ u32 rss_type = igc_rss_type(rx_desc);
+
+ skb_set_hash(skb, rss_hash, igc_rss_type_table[rss_type]);
+ }
}

static void igc_rx_vlan(struct igc_ring *rx_ring,
@@ -6554,6 +6576,7 @@ static int igc_probe(struct pci_dev *pdev,
netdev->features |= NETIF_F_TSO;
netdev->features |= NETIF_F_TSO6;
netdev->features |= NETIF_F_TSO_ECN;
+ netdev->features |= NETIF_F_RXHASH;
netdev->features |= NETIF_F_RXCSUM;
netdev->features |= NETIF_F_HW_CSUM;
netdev->features |= NETIF_F_SCTP_CRC;