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

[Pavan Nikhilesh Bhagavatula]

>On 18/03/2020 21:35, jerinj at marvell.com wrote:
>> From: Pavan Nikhilesh <pbhagavatula at 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 at marvell.com>
>> Signed-off-by: Nithin Dabilpuram <ndabilpuram at marvell.com>
>> Signed-off-by: Kiran Kumar K <kirankumark at 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.

Ack will remove in v2 for x86.

>
>> +	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.
>

How would be take the benefit of rte_lpm_lookupx4 without unrolling the loop?.
Also, in future if we are using rte_rib and fib with a CPU supporting wider SIMD we might
need to unroll them further (AVX256 AND 512 currently rte_lpm_lookup uses only 128bit
since it is only uses SSE extension). 

>
>> +	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
>>