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

From: John Fastabend <[email-masked]>
Date: Sun, 23 Apr 2023 07:46:11 -0700

Jesper Dangaard Brouer wrote:
> 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 <[email-masked]>
> ---
>  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]);

Just curious why not copy the logic from the other driver fms10k, ice, ect.

	skb_set_hash(skb, le32_to_cpu(rx_desc->wb.lower.hi_dword.rss),
		     (IXGBE_RSS_L4_TYPES_MASK & (1ul << rss_type)) ?
		     PKT_HASH_TYPE_L4 : PKT_HASH_TYPE_L3);

avoiding the table logic. Do the driver folks care?