Commit 197dbf24 authored Nov 20, 2019 by Paolo Abeni Committed by David S. Miller Nov 21, 2019

ipv6: introduce and uses route look hints for list input.



When doing RX batch packet processing, we currently always repeat
the route lookup for each ingress packet. When no custom rules are
in place, and there aren't routes depending on source addresses,
we know that packets with the same destination address will use
the same dst.

This change tries to avoid per packet route lookup caching
the destination address of the latest successful lookup, and
reusing it for the next packet when the above conditions are
in place. Ingress traffic for most servers should fit.

The measured performance delta under UDP flood vs a recvmmsg
receiver is as follow:

vanilla		patched		delta
Kpps		Kpps		%
1431		1674		+17

In the worst-case scenario - each packet has a different
destination address - the performance delta is within noise
range.

v3 -> v4:
 - support hints for SUBFLOW build, too (David A.)
 - several style fixes (Eric)

v2 -> v3:
 - add fib6_has_custom_rules() helpers (David A.)
 - add ip6_extract_route_hint() helper (Edward C.)
 - use hint directly in ip6_list_rcv_finish() (Willem)

v1 -> v2:
 - fix build issue with !CONFIG_IPV6_MULTIPLE_TABLES
 - fix potential race when fib6_has_custom_rules is set
   while processing a packet batch

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b9b33e7c

net/ipv6/ip6_input.c

+24 −2

Original line number	Diff line number	Diff line
		@@ -86,11 +86,27 @@ static void ip6_sublist_rcv_finish(struct list_head *head)
		}
		}

		static bool ip6_can_use_hint(const struct sk_buff *skb,
		const struct sk_buff *hint)
		{
		return hint && !skb_dst(skb) &&
		ipv6_addr_equal(&ipv6_hdr(hint)->daddr, &ipv6_hdr(skb)->daddr);
		}

		static struct sk_buff ip6_extract_route_hint(const struct net net,
		struct sk_buff *skb)
		{
		if (fib6_routes_require_src(net) \|\| fib6_has_custom_rules(net))
		return NULL;

		return skb;
		}

		static void ip6_list_rcv_finish(struct net net, struct sock sk,
		struct list_head *head)
		{
		struct sk_buff skb, next, *hint = NULL;
		struct dst_entry *curr_dst = NULL;
		struct sk_buff skb, next;
		struct list_head sublist;

		INIT_LIST_HEAD(&sublist);
		@@ -104,9 +120,15 @@ static void ip6_list_rcv_finish(struct net net, struct sock sk,
		skb = l3mdev_ip6_rcv(skb);
		if (!skb)
		continue;

		if (ip6_can_use_hint(skb, hint))
		skb_dst_copy(skb, hint);
		else
		ip6_rcv_finish_core(net, sk, skb);
		dst = skb_dst(skb);
		if (curr_dst != dst) {
		hint = ip6_extract_route_hint(net, skb);

		/* dispatch old sublist */
		if (!list_empty(&sublist))
		ip6_sublist_rcv_finish(&sublist);

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