netdev - [PATCH net-next 6/6] ipv6: avoid cache line dirtying in ipv6_dev_get

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Message-Id: <20171008023028.32071-7-edumazet@google.com>
Date:   Sat,  7 Oct 2017 19:30:28 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: [PATCH net-next 6/6] ipv6: avoid cache line dirtying in ipv6_dev_get_saddr()

By extending the rcu section a bit, we can avoid these
very expensive in6_ifa_put()/in6_ifa_hold() calls
done in __ipv6_dev_get_saddr() and ipv6_dev_get_saddr()

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv6/addrconf.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 20c3ca777529fc49ebf749ca6f7d8c2451258d55..cab3faad2bf1354c1241a11ac27178ea675aed55 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1608,11 +1608,6 @@ static int __ipv6_dev_get_saddr(struct net *net,
 				}
 				break;
 			} else if (minihiscore < miniscore) {
-				if (hiscore->ifa)
-					in6_ifa_put(hiscore->ifa);
-
-				in6_ifa_hold(score->ifa);
-
 				swap(hiscore, score);
 				hiscore_idx = 1 - hiscore_idx;
 
@@ -1660,6 +1655,7 @@ int ipv6_dev_get_saddr(struct net *net, const struct net_device *dst_dev,
 	int dst_type;
 	bool use_oif_addr = false;
 	int hiscore_idx = 0;
+	int ret = 0;
 
 	dst_type = __ipv6_addr_type(daddr);
 	dst.addr = daddr;
@@ -1735,15 +1731,14 @@ int ipv6_dev_get_saddr(struct net *net, const struct net_device *dst_dev,
 	}
 
 out:
-	rcu_read_unlock();
-
 	hiscore = &scores[hiscore_idx];
 	if (!hiscore->ifa)
-		return -EADDRNOTAVAIL;
+		ret = -EADDRNOTAVAIL;
+	else
+		*saddr = hiscore->ifa->addr;
 
-	*saddr = hiscore->ifa->addr;
-	in6_ifa_put(hiscore->ifa);
-	return 0;
+	rcu_read_unlock();
+	return ret;
 }
 EXPORT_SYMBOL(ipv6_dev_get_saddr);
 
-- 
2.14.2.920.gcf0c67979c-goog