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Date: Tue, 14 Feb 2023 14:21:00 +0100
From: Alexander Lobakin <alexandr.lobakin@...el.com>
To: Jesper Dangaard Brouer <brouer@...hat.com>
CC: <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
Stanislav Fomichev <sdf@...gle.com>, <martin.lau@...nel.org>,
<ast@...nel.org>, <daniel@...earbox.net>,
<yoong.siang.song@...el.com>, <anthony.l.nguyen@...el.com>,
<intel-wired-lan@...ts.osuosl.org>, <xdp-hints@...-project.net>
Subject: Re: [PATCH bpf-next V1] igc: enable and fix RX hash usage by netstack
From: Jesper Dangaard Brouer <brouer@...hat.com>
Date: Fri, 10 Feb 2023 16:07:59 +0100
> 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.
[...]
> @@ -311,6 +311,58 @@ 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 0xF
GENMASK()?
> +
> +/* igc_rss_type - Rx descriptor RSS type field */
> +static inline u8 igc_rss_type(union igc_adv_rx_desc *rx_desc)
Why use types shorter than u32 on the stack?
Why this union is not const here, since there are no modifications?
> +{
> + /* RSS Type 4-bit number: 0-9 (above 9 is reserved) */
> + return rx_desc->wb.lower.lo_dword.hs_rss.pkt_info & IGC_RSS_TYPE_MASK;
The most important I wanted to mention: doesn't this function make the
CPU read the uncached field again, while you could just read it once
onto the stack and then extract all such data from there?
> +}
> +
> +/* Packet header type identified by hardware (when BIT(11) is zero).
> + * Even when UDP ports are not part of RSS hash HW still parse and mark UDP bits
> + */
> +enum igc_pkt_type_bits {
> + IGC_PKT_TYPE_HDR_IPV4 = BIT(0),
> + IGC_PKT_TYPE_HDR_IPV4_WITH_OPT= BIT(1), /* IPv4 Hdr includes IP options */
> + IGC_PKT_TYPE_HDR_IPV6 = BIT(2),
> + IGC_PKT_TYPE_HDR_IPV6_WITH_EXT= BIT(3), /* IPv6 Hdr includes extensions */
> + IGC_PKT_TYPE_HDR_L4_TCP = BIT(4),
> + IGC_PKT_TYPE_HDR_L4_UDP = BIT(5),
> + IGC_PKT_TYPE_HDR_L4_SCTP= BIT(6),
> + IGC_PKT_TYPE_HDR_NFS = BIT(7),
> + /* Above only valid when BIT(11) is zero */
> + IGC_PKT_TYPE_L2 = BIT(11),
> + IGC_PKT_TYPE_VLAN = BIT(12),
> + IGC_PKT_TYPE_MASK = 0x1FFF, /* 13-bits */
Also GENMASK().
> +};
> +
> +/* igc_pkt_type - Rx descriptor Packet type field */
> +static inline u16 igc_pkt_type(union igc_adv_rx_desc *rx_desc)
Also short types and consts.
> +{
> + u32 data = le32_to_cpu(rx_desc->wb.lower.lo_dword.data);
> + /* Packet type is 13-bits - as bits (16:4) in lower.lo_dword*/
> + u16 pkt_type = (data >> 4) & IGC_PKT_TYPE_MASK;
Perfect candidate for FIELD_GET(). No, even for le32_get_bits().
Also my note above about excessive expensive reads.
> +
> + return pkt_type;
> +}
> +
> /* 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 8b572cd2c350..42a072509d2a 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -1677,14 +1677,40 @@ 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 */
> +struct igc_rss_type {
> + u8 hash_type; /* can contain enum pkt_hash_types */
Why make a struct for one field? + short type note
> +} igc_rss_type_table[IGC_RSS_TYPE_MAX_TABLE] = {
> + [IGC_RSS_TYPE_NO_HASH].hash_type = PKT_HASH_TYPE_L2,
> + [IGC_RSS_TYPE_HASH_TCP_IPV4].hash_type = PKT_HASH_TYPE_L4,
> + [IGC_RSS_TYPE_HASH_IPV4].hash_type = PKT_HASH_TYPE_L3,
> + [IGC_RSS_TYPE_HASH_TCP_IPV6].hash_type = PKT_HASH_TYPE_L4,
> + [IGC_RSS_TYPE_HASH_IPV6_EX].hash_type = PKT_HASH_TYPE_L3,
> + [IGC_RSS_TYPE_HASH_IPV6].hash_type = PKT_HASH_TYPE_L3,
> + [IGC_RSS_TYPE_HASH_TCP_IPV6_EX].hash_type = PKT_HASH_TYPE_L4,
> + [IGC_RSS_TYPE_HASH_UDP_IPV4].hash_type = PKT_HASH_TYPE_L4,
> + [IGC_RSS_TYPE_HASH_UDP_IPV6].hash_type = PKT_HASH_TYPE_L4,
> + [IGC_RSS_TYPE_HASH_UDP_IPV6_EX].hash_type = PKT_HASH_TYPE_L4,
> + [10].hash_type = PKT_HASH_TYPE_L2, /* RSS Type above 9 "Reserved" by HW */
> + [11].hash_type = PKT_HASH_TYPE_L2,
> + [12].hash_type = PKT_HASH_TYPE_L2,
> + [13].hash_type = PKT_HASH_TYPE_L2,
> + [14].hash_type = PKT_HASH_TYPE_L2,
> + [15].hash_type = PKT_HASH_TYPE_L2,
Why define those empty if you could do a bound check in the code
instead? E.g. `if (unlikely(bigger_than_9)) return PKT_HASH_TYPE_L2`.
> +};
> +
> 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) {
if (!(feature & HASH))
return;
and -1 indent level?
> + u32 rss_hash = le32_to_cpu(rx_desc->wb.lower.hi_dword.rss);
> + u8 rss_type = igc_rss_type(rx_desc);
> + enum pkt_hash_types hash_type;
> +
> + hash_type = igc_rss_type_table[rss_type].hash_type;
> + skb_set_hash(skb, rss_hash, hash_type);
> + }
> }
[...]
Thanks,
Olek
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