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Subject[PATCH 01/14] ipv6: optimise dst referencing
Date
__ip6_make_skb() initialises skb's dst by taking an additional reference
to cork->dst. However, cork->dst comes into the function holding a ref,
which will be put shortly at the end of the function in
ip6_cork_release().

Avoid this extra pair of get/put atomics by stealing cork->dst and
NULL'ing the field, ip6_cork_release() already handles zero values.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
net/ipv6/ip6_output.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2995f8d89e7e..14d607ccfeea 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1807,6 +1807,15 @@ int ip6_append_data(struct sock *sk,
}
EXPORT_SYMBOL_GPL(ip6_append_data);

+static void ip6_cork_steal_dst(struct sk_buff *skb, struct inet_cork_full *cork)
+{
+ struct dst_entry *dst = cork->base.dst;
+
+ cork->base.dst = NULL;
+ cork->base.flags &= ~IPCORK_ALLFRAG;
+ skb_dst_set(skb, dst);
+}
+
static void ip6_cork_release(struct inet_cork_full *cork,
struct inet6_cork *v6_cork)
{
@@ -1889,7 +1898,7 @@ struct sk_buff *__ip6_make_skb(struct sock *sk,

skb->tstamp = cork->base.transmit_time;

- skb_dst_set(skb, dst_clone(&rt->dst));
+ ip6_cork_steal_dst(skb, cork);
IP6_UPD_PO_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUT, skb->len);
if (proto == IPPROTO_ICMPV6) {
struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));
--
2.34.1
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