[PATCH net-next] ipv6: optimize fl6_update_dst()

[PATCH net-next] ipv6: optimize fl6_update_dst()

[Eric Dumazet]

fl6_update_dst() is called for every TCP (and others) transmit,
and is a nop for common cases.

Split it in two parts :

1) fl6_update_dst() inline helper, small and fast.

2) __fl6_update_dst() for the exception, out of line.

Small size increase to get better TX performance.

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 2/2 grow/shrink: 8/0 up/down: 296/-125 (171)
Function                                     old     new   delta
__fl6_update_dst                               -     104    +104
rawv6_sendmsg                               2244    2284     +40
udpv6_sendmsg                               3013    3043     +30
tcp_v6_connect                              1514    1534     +20
cookie_v6_check                             1501    1519     +18
ip6_datagram_dst_update                      673     690     +17
inet6_sk_rebuild_header                      499     516     +17
inet6_csk_route_socket                       507     524     +17
inet6_csk_route_req                          343     360     +17
__pfx___fl6_update_dst                         -      16     +16
__pfx_fl6_update_dst                          16       -     -16
fl6_update_dst                               109       -    -109
Total: Before=22570304, After=22570475, chg +0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/ipv6.h | 16 +++++++++++++---
 net/ipv6/exthdrs.c | 14 +++++++-------
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index c7f597da01cd92293b9ffbd9e692dea75fd581b8..cf2203ff2bfd2b42381aba196578cd2668796c8b 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -1174,9 +1174,19 @@ int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset, int target,
 
 int ipv6_find_tlv(const struct sk_buff *skb, int offset, int type);
 
-struct in6_addr *fl6_update_dst(struct flowi6 *fl6,
-				const struct ipv6_txoptions *opt,
-				struct in6_addr *orig);
+struct in6_addr *__fl6_update_dst(struct flowi6 *fl6,
+				  const struct ipv6_txoptions *opt,
+				  struct in6_addr *orig);
+
+static inline struct in6_addr *
+fl6_update_dst(struct flowi6 *fl6, const struct ipv6_txoptions *opt,
+	       struct in6_addr *orig)
+{
+	if (likely(!opt))
+		return NULL;
+
+	return __fl6_update_dst(fl6, opt, orig);
+}
 
 /*
  *	socket options (ipv6_sockglue.c)
diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 54088fa0c09d068d35779e3cafd721cd24e00ea8..ae173abdca9965fb4be2a0565c81d1e24c5535c7 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -1336,21 +1336,21 @@ struct ipv6_txoptions *__ipv6_fixup_options(struct ipv6_txoptions *opt_space,
 EXPORT_SYMBOL_GPL(__ipv6_fixup_options);
 
 /**
- * fl6_update_dst - update flowi destination address with info given
+ * __fl6_update_dst - update flowi destination address with info given
  *                  by srcrt option, if any.
  *
  * @fl6: flowi6 for which daddr is to be updated
  * @opt: struct ipv6_txoptions in which to look for srcrt opt
  * @orig: copy of original daddr address if modified
  *
- * Returns NULL if no txoptions or no srcrt, otherwise returns orig
+ * Returns NULL if no srcrt or invalid srcrt type, otherwise returns orig
  * and initial value of fl6->daddr set in orig
  */
-struct in6_addr *fl6_update_dst(struct flowi6 *fl6,
-				const struct ipv6_txoptions *opt,
-				struct in6_addr *orig)
+struct in6_addr *__fl6_update_dst(struct flowi6 *fl6,
+				  const struct ipv6_txoptions *opt,
+				  struct in6_addr *orig)
 {
-	if (!opt || !opt->srcrt)
+	if (!opt->srcrt)
 		return NULL;
 
 	*orig = fl6->daddr;
@@ -1374,4 +1374,4 @@ struct in6_addr *fl6_update_dst(struct flowi6 *fl6,
 
 	return orig;
 }
-EXPORT_SYMBOL_GPL(fl6_update_dst);
+EXPORT_SYMBOL_GPL(__fl6_update_dst);
-- 
2.53.0.rc1.217.geba53bf80e-goog

Re: [PATCH net-next] ipv6: optimize fl6_update_dst()

[Jakub Kicinski]

On Wed, 28 Jan 2026 18:55:47 +0000 Eric Dumazet wrote:
> - * Returns NULL if no txoptions or no srcrt, otherwise returns orig
> + * Returns NULL if no srcrt or invalid srcrt type, otherwise returns orig

I'm gonna take this opportunity to update this line to Return:
in accordance with kdoc rules, hope you don't mind. Applied.

Re: [PATCH net-next] ipv6: optimize fl6_update_dst()

[Eric Dumazet]

On Fri, Jan 30, 2026 at 3:48 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 28 Jan 2026 18:55:47 +0000 Eric Dumazet wrote:
> > - * Returns NULL if no txoptions or no srcrt, otherwise returns orig
> > + * Returns NULL if no srcrt or invalid srcrt type, otherwise returns orig
>
> I'm gonna take this opportunity to update this line to Return:
> in accordance with kdoc rules, hope you don't mind. Applied.

Sure thing, thank you!