[xdp-hints] Re: [PATCH bpf-next v6 06/18] ice: Support RX hash XDP hint

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Thu, Oct 12, 2023 at 07:05:12PM +0200, Larysa Zaremba wrote:
> RX hash XDP hint requests both hash value and type.
> Type is XDP-specific, so we need a separate way to map
> these values to the hardware ptypes, so create a lookup table.
> 
> Instead of creating a new long list, reuse contents
> of ice_decode_rx_desc_ptype[] through preprocessor.
> 
> Current hash type enum does not contain ICMP packet type,
> but ice devices support it, so also add a new type into core code.
> 
> Then use previously refactored code and create a function
> that allows XDP code to read RX hash.
> 
> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> ---

(...)

> +
> +/**
> + * ice_xdp_rx_hash_type - Get XDP-specific hash type from the RX descriptor
> + * @eop_desc: End of Packet descriptor
> + */
> +static enum xdp_rss_hash_type
> +ice_xdp_rx_hash_type(const union ice_32b_rx_flex_desc *eop_desc)
> +{
> +	u16 ptype = ice_get_ptype(eop_desc);
> +
> +	if (unlikely(ptype >= ICE_NUM_DEFINED_PTYPES))
> +		return 0;
> +
> +	return ice_ptype_to_xdp_hash[ptype];
> +}
> +
> +/**
> + * ice_xdp_rx_hash - RX hash XDP hint handler
> + * @ctx: XDP buff pointer
> + * @hash: hash destination address
> + * @rss_type: XDP hash type destination address
> + *
> + * Copy RX hash (if available) and its type to the destination address.
> + */
> +static int ice_xdp_rx_hash(const struct xdp_md *ctx, u32 *hash,
> +			   enum xdp_rss_hash_type *rss_type)
> +{
> +	const struct ice_xdp_buff *xdp_ext = (void *)ctx;
> +
> +	*hash = ice_get_rx_hash(xdp_ext->pkt_ctx.eop_desc);
> +	*rss_type = ice_xdp_rx_hash_type(xdp_ext->pkt_ctx.eop_desc);
> +	if (!likely(*hash))
> +		return -ENODATA;

maybe i have missed previous discussions, but why hash/rss_type are copied
regardless of them being available? if i am missing something can you
elaborate on that?

also, !likely() construct looks tricky to me, I am not sure what was the
intent behind it. other callbacks return -ENODATA in case NETIF_F_RXHASH
is missing from dev->features.

> +
> +	return 0;
> +}
> +
>  const struct xdp_metadata_ops ice_xdp_md_ops = {
>  	.xmo_rx_timestamp		= ice_xdp_rx_hw_ts,
> +	.xmo_rx_hash			= ice_xdp_rx_hash,
>  };
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 349c36fb5fd8..eb77040b4825 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -427,6 +427,7 @@ enum xdp_rss_hash_type {
>  	XDP_RSS_L4_UDP		= BIT(5),
>  	XDP_RSS_L4_SCTP		= BIT(6),
>  	XDP_RSS_L4_IPSEC	= BIT(7), /* L4 based hash include IPSEC SPI */
> +	XDP_RSS_L4_ICMP		= BIT(8),
>  
>  	/* Second part: RSS hash type combinations used for driver HW mapping */
>  	XDP_RSS_TYPE_NONE            = 0,
> @@ -442,11 +443,13 @@ enum xdp_rss_hash_type {
>  	XDP_RSS_TYPE_L4_IPV4_UDP     = XDP_RSS_L3_IPV4 | XDP_RSS_L4 | XDP_RSS_L4_UDP,
>  	XDP_RSS_TYPE_L4_IPV4_SCTP    = XDP_RSS_L3_IPV4 | XDP_RSS_L4 | XDP_RSS_L4_SCTP,
>  	XDP_RSS_TYPE_L4_IPV4_IPSEC   = XDP_RSS_L3_IPV4 | XDP_RSS_L4 | XDP_RSS_L4_IPSEC,
> +	XDP_RSS_TYPE_L4_IPV4_ICMP    = XDP_RSS_L3_IPV4 | XDP_RSS_L4 | XDP_RSS_L4_ICMP,
>  
>  	XDP_RSS_TYPE_L4_IPV6_TCP     = XDP_RSS_L3_IPV6 | XDP_RSS_L4 | XDP_RSS_L4_TCP,
>  	XDP_RSS_TYPE_L4_IPV6_UDP     = XDP_RSS_L3_IPV6 | XDP_RSS_L4 | XDP_RSS_L4_UDP,
>  	XDP_RSS_TYPE_L4_IPV6_SCTP    = XDP_RSS_L3_IPV6 | XDP_RSS_L4 | XDP_RSS_L4_SCTP,
>  	XDP_RSS_TYPE_L4_IPV6_IPSEC   = XDP_RSS_L3_IPV6 | XDP_RSS_L4 | XDP_RSS_L4_IPSEC,
> +	XDP_RSS_TYPE_L4_IPV6_ICMP    = XDP_RSS_L3_IPV6 | XDP_RSS_L4 | XDP_RSS_L4_ICMP,
>  
>  	XDP_RSS_TYPE_L4_IPV6_TCP_EX  = XDP_RSS_TYPE_L4_IPV6_TCP  | XDP_RSS_L3_DYNHDR,
>  	XDP_RSS_TYPE_L4_IPV6_UDP_EX  = XDP_RSS_TYPE_L4_IPV6_UDP  | XDP_RSS_L3_DYNHDR,
> -- 
> 2.41.0
>