Re: [dpdk-dev] [PATCH v1 20/26] node: ipv4 lookup for x86

[Ray Kinsella <mdr@ashroe.eu>]

On 18/03/2020 21:35, jerinj@marvell.com wrote:
> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
> 
> Add IPv4 lookup process function for ip4_lookup
> rte_node. This node performs LPM lookup using x86_64
> vector supported RTE_LPM API on every packet received
> and forwards it to a next node that is identified by
> lookup result.
> 
> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
> Signed-off-by: Kiran Kumar K <kirankumark@marvell.com>
> ---
>  lib/librte_node/ip4_lookup.c | 245 +++++++++++++++++++++++++++++++++++
>  1 file changed, 245 insertions(+)
> 
> diff --git a/lib/librte_node/ip4_lookup.c b/lib/librte_node/ip4_lookup.c
> index d7fcd1158..c003e9c91 100644
> --- a/lib/librte_node/ip4_lookup.c
> +++ b/lib/librte_node/ip4_lookup.c
> @@ -264,6 +264,251 @@ ip4_lookup_node_process(struct rte_graph *graph, struct rte_node *node,
>  	return nb_objs;
>  }
>  
> +#elif defined(RTE_ARCH_X86)
> +
> +/* X86 SSE */
> +static uint16_t
> +ip4_lookup_node_process(struct rte_graph *graph, struct rte_node *node,
> +			void **objs, uint16_t nb_objs)
> +{
> +	struct rte_mbuf *mbuf0, *mbuf1, *mbuf2, *mbuf3, **pkts;
> +	rte_edge_t next0, next1, next2, next3, next_index;
> +	struct rte_ipv4_hdr *ipv4_hdr;
> +	struct rte_ether_hdr *eth_hdr;
> +	uint32_t ip0, ip1, ip2, ip3;
> +	void **to_next, **from;
> +	uint16_t last_spec = 0;
> +	uint16_t n_left_from;
> +	struct rte_lpm *lpm;
> +	uint16_t held = 0;
> +	uint32_t drop_nh;
> +	rte_xmm_t dst;
> +	__m128i dip; /* SSE register */
> +	int rc, i;
> +
> +	/* Speculative next */
> +	next_index = RTE_NODE_IP4_LOOKUP_NEXT_REWRITE;
> +	/* Drop node */
> +	drop_nh = ((uint32_t)RTE_NODE_IP4_LOOKUP_NEXT_PKT_DROP) << 16;
> +
> +	/* Get socket specific LPM from ctx */
> +	lpm = *((struct rte_lpm **)node->ctx);
> +
> +	pkts = (struct rte_mbuf **)objs;
> +	from = objs;
> +	n_left_from = nb_objs;

I doubt this initial prefetch of the first 4 packets has any benefit. 

> +	if (n_left_from >= 4) {
> +		for (i = 0; i < 4; i++) {
> +			rte_prefetch0(rte_pktmbuf_mtod(pkts[i],
> +						       struct rte_ether_hdr *) +
> +				      1);
> +		}
> +	}
> +
> +	/* Get stream for the speculated next node */
> +	to_next = rte_node_next_stream_get(graph, node, next_index, nb_objs);

Suggest you don't reuse the hand-unrolling optimization from FD.io VPP. 
I have never found any performance benefit from them, and they make the code unnecessarily verbose. 


> +	while (n_left_from >= 4) {
> +		/* Prefetch next-next mbufs */
> +		if (likely(n_left_from >= 11)) {
> +			rte_prefetch0(pkts[8]);
> +			rte_prefetch0(pkts[9]);
> +			rte_prefetch0(pkts[10]);
> +			rte_prefetch0(pkts[11]);
> +		}
> +
> +		/* Prefetch next mbuf data */
> +		if (likely(n_left_from >= 7)) {
> +			rte_prefetch0(rte_pktmbuf_mtod(pkts[4],
> +						       struct rte_ether_hdr *) +
> +				      1);
> +			rte_prefetch0(rte_pktmbuf_mtod(pkts[5],
> +						       struct rte_ether_hdr *) +
> +				      1);
> +			rte_prefetch0(rte_pktmbuf_mtod(pkts[6],
> +						       struct rte_ether_hdr *) +
> +				      1);
> +			rte_prefetch0(rte_pktmbuf_mtod(pkts[7],
> +						       struct rte_ether_hdr *) +
> +				      1);
> +		}
> +
> +		mbuf0 = pkts[0];
> +		mbuf1 = pkts[1];
> +		mbuf2 = pkts[2];
> +		mbuf3 = pkts[3];
> +
> +		pkts += 4;
> +		n_left_from -= 4;
> +
> +		/* Extract DIP of mbuf0 */
> +		eth_hdr = rte_pktmbuf_mtod(mbuf0, struct rte_ether_hdr *);
> +		ipv4_hdr = (struct rte_ipv4_hdr *)(eth_hdr + 1);
> +		ip0 = ipv4_hdr->dst_addr;
> +		/* Extract cksum, ttl as ipv4 hdr is in cache */
> +		rte_node_mbuf_priv1(mbuf0)->cksum = ipv4_hdr->hdr_checksum;
> +		rte_node_mbuf_priv1(mbuf0)->ttl = ipv4_hdr->time_to_live;
> +
> +		/* Extract DIP of mbuf1 */
> +		eth_hdr = rte_pktmbuf_mtod(mbuf1, struct rte_ether_hdr *);
> +		ipv4_hdr = (struct rte_ipv4_hdr *)(eth_hdr + 1);
> +		ip1 = ipv4_hdr->dst_addr;
> +		/* Extract cksum, ttl as ipv4 hdr is in cache */
> +		rte_node_mbuf_priv1(mbuf1)->cksum = ipv4_hdr->hdr_checksum;
> +		rte_node_mbuf_priv1(mbuf1)->ttl = ipv4_hdr->time_to_live;
> +
> +		/* Extract DIP of mbuf2 */
> +		eth_hdr = rte_pktmbuf_mtod(mbuf2, struct rte_ether_hdr *);
> +		ipv4_hdr = (struct rte_ipv4_hdr *)(eth_hdr + 1);
> +		ip2 = ipv4_hdr->dst_addr;
> +		/* Extract cksum, ttl as ipv4 hdr is in cache */
> +		rte_node_mbuf_priv1(mbuf2)->cksum = ipv4_hdr->hdr_checksum;
> +		rte_node_mbuf_priv1(mbuf2)->ttl = ipv4_hdr->time_to_live;
> +
> +		/* Extract DIP of mbuf3 */
> +		eth_hdr = rte_pktmbuf_mtod(mbuf3, struct rte_ether_hdr *);
> +		ipv4_hdr = (struct rte_ipv4_hdr *)(eth_hdr + 1);
> +		ip3 = ipv4_hdr->dst_addr;
> +
> +		/* Prepare for lookup x4 */
> +		dip = _mm_set_epi32(ip3, ip2, ip1, ip0);
> +
> +		/* Byte swap 4 IPV4 addresses. */
> +		const __m128i bswap_mask = _mm_set_epi8(
> +			12, 13, 14, 15, 8, 9, 10, 11, 4, 5, 6, 7, 0, 1, 2, 3);
> +		dip = _mm_shuffle_epi8(dip, bswap_mask);
> +
> +		/* Extract cksum, ttl as ipv4 hdr is in cache */
> +		rte_node_mbuf_priv1(mbuf3)->cksum = ipv4_hdr->hdr_checksum;
> +		rte_node_mbuf_priv1(mbuf3)->ttl = ipv4_hdr->time_to_live;
> +
> +		/* Perform LPM lookup to get NH and next node */
> +		rte_lpm_lookupx4(lpm, dip, dst.u32, drop_nh);
> +
> +		/* Extract next node id and NH */
> +		rte_node_mbuf_priv1(mbuf0)->nh = dst.u32[0] & 0xFFFF;
> +		next0 = (dst.u32[0] >> 16);
> +
> +		rte_node_mbuf_priv1(mbuf1)->nh = dst.u32[1] & 0xFFFF;
> +		next1 = (dst.u32[1] >> 16);
> +
> +		rte_node_mbuf_priv1(mbuf2)->nh = dst.u32[2] & 0xFFFF;
> +		next2 = (dst.u32[2] >> 16);
> +
> +		rte_node_mbuf_priv1(mbuf3)->nh = dst.u32[3] & 0xFFFF;
> +		next3 = (dst.u32[3] >> 16);
> +
> +		/* Enqueue four to next node */
> +		rte_edge_t fix_spec =
> +			(next_index ^ next0) | (next_index ^ next1) |
> +			(next_index ^ next2) | (next_index ^ next3);
> +
> +		if (unlikely(fix_spec)) {
> +			/* Copy things successfully speculated till now */
> +			rte_memcpy(to_next, from, last_spec * sizeof(from[0]));
> +			from += last_spec;
> +			to_next += last_spec;
> +			held += last_spec;
> +			last_spec = 0;
> +
> +			/* Next0 */
> +			if (next_index == next0) {
> +				to_next[0] = from[0];
> +				to_next++;
> +				held++;
> +			} else {
> +				rte_node_enqueue_x1(graph, node, next0,
> +						    from[0]);
> +			}
> +
> +			/* Next1 */
> +			if (next_index == next1) {
> +				to_next[0] = from[1];
> +				to_next++;
> +				held++;
> +			} else {
> +				rte_node_enqueue_x1(graph, node, next1,
> +						    from[1]);
> +			}
> +
> +			/* Next2 */
> +			if (next_index == next2) {
> +				to_next[0] = from[2];
> +				to_next++;
> +				held++;
> +			} else {
> +				rte_node_enqueue_x1(graph, node, next2,
> +						    from[2]);
> +			}
> +
> +			/* Next3 */
> +			if (next_index == next3) {
> +				to_next[0] = from[3];
> +				to_next++;
> +				held++;
> +			} else {
> +				rte_node_enqueue_x1(graph, node, next3,
> +						    from[3]);
> +			}
> +
> +			from += 4;
> +
> +		} else {
> +			last_spec += 4;
> +		}
> +	}
> +
> +	while (n_left_from > 0) {
> +		uint32_t next_hop;
> +
> +		mbuf0 = pkts[0];
> +
> +		pkts += 1;
> +		n_left_from -= 1;
> +
> +		/* Extract DIP of mbuf0 */
> +		eth_hdr = rte_pktmbuf_mtod(mbuf0, struct rte_ether_hdr *);
> +		ipv4_hdr = (struct rte_ipv4_hdr *)(eth_hdr + 1);
> +		/* Extract cksum, ttl as ipv4 hdr is in cache */
> +		rte_node_mbuf_priv1(mbuf0)->cksum = ipv4_hdr->hdr_checksum;
> +		rte_node_mbuf_priv1(mbuf0)->ttl = ipv4_hdr->time_to_live;
> +
> +		rc = rte_lpm_lookup(lpm, rte_be_to_cpu_32(ipv4_hdr->dst_addr),
> +				    &next_hop);
> +		next_hop = (rc == 0) ? next_hop : drop_nh;
> +
> +		rte_node_mbuf_priv1(mbuf0)->nh = next_hop & 0xFFFF;
> +		next0 = (next_hop >> 16);
> +
> +		if (unlikely(next_index ^ next0)) {
> +			/* Copy things successfully speculated till now */
> +			rte_memcpy(to_next, from, last_spec * sizeof(from[0]));
> +			from += last_spec;
> +			to_next += last_spec;
> +			held += last_spec;
> +			last_spec = 0;
> +
> +			rte_node_enqueue_x1(graph, node, next0, from[0]);
> +			from += 1;
> +		} else {
> +			last_spec += 1;
> +		}
> +	}
> +
> +	/* !!! Home run !!! */
> +	if (likely(last_spec == nb_objs)) {
> +		rte_node_next_stream_move(graph, node, next_index);
> +		return nb_objs;
> +	}
> +
> +	held += last_spec;
> +	/* Copy things successfully speculated till now */
> +	rte_memcpy(to_next, from, last_spec * sizeof(from[0]));
> +	rte_node_next_stream_put(graph, node, next_index, held);
> +
> +	return nb_objs;
> +}
> +
>  #else
>  
>  static uint16_t
>