netdev - [PATCH net-next v3 1/2] ipv6: introduce and uses route look hints for list input

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Message-Id: <422ebfbf2fcb8a6ce23bcd97ab1f7c3a0c633cbd.1574165644.git.pabeni@redhat.com>
Date:   Tue, 19 Nov 2019 15:38:36 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Edward Cree <ecree@...arflare.com>,
        David Ahern <dsahern@...il.com>
Subject: [PATCH net-next v3 1/2] 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. If policy routing is
configured, and IPV6_SUBTREES is disabled at build time, 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.

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@...hat.com>
---
 include/net/ip6_fib.h |  9 +++++++++
 net/ipv6/ip6_input.c  | 26 ++++++++++++++++++++++++--
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 5d1615463138..9ab60611b97b 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -502,6 +502,11 @@ static inline bool fib6_metric_locked(struct fib6_info *f6i, int metric)
 }
 
 #ifdef CONFIG_IPV6_MULTIPLE_TABLES
+static inline bool fib6_has_custom_rules(struct net *net)
+{
+	return net->ipv6.fib6_has_custom_rules;
+}
+
 int fib6_rules_init(void);
 void fib6_rules_cleanup(void);
 bool fib6_rule_default(const struct fib_rule *rule);
@@ -527,6 +532,10 @@ static inline bool fib6_rules_early_flow_dissect(struct net *net,
 	return true;
 }
 #else
+static inline bool fib6_has_custom_rules(struct net *net)
+{
+	return 0;
+}
 static inline int               fib6_rules_init(void)
 {
 	return 0;
diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index ef7f707d9ae3..792b52aa9fc9 100644
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -59,6 +59,7 @@ static void ip6_rcv_finish_core(struct net *net, struct sock *sk,
 			INDIRECT_CALL_2(edemux, tcp_v6_early_demux,
 					udp_v6_early_demux, skb);
 	}
+
 	if (!skb_valid_dst(skb))
 		ip6_route_input(skb);
 }
@@ -86,11 +87,26 @@ static void ip6_sublist_rcv_finish(struct list_head *head)
 	}
 }
 
+static bool ip6_can_use_hint(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(struct net *net,
+					      struct sk_buff *skb)
+{
+	if (IS_ENABLED(IPV6_SUBTREES) || 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;
-		ip6_rcv_finish_core(net, sk, skb);
+
+		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);
-- 
2.21.0