netdev - [PATCH net-next 1/4] rtnl: add helper to check if rtnl group has listeners

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Message-Id: <20231201204314.220543-2-pctammela@mojatatu.com>
Date: Fri,  1 Dec 2023 17:43:11 -0300
From: Pedro Tammela <pctammela@...atatu.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	jhs@...atatu.com,
	xiyou.wangcong@...il.com,
	jiri@...nulli.us,
	marcelo.leitner@...il.com,
	vladbu@...dia.com,
	Victor Nogueira <victor@...atatu.com>,
	Pedro Tammela <pctammela@...atatu.com>
Subject: [PATCH net-next 1/4] rtnl: add helper to check if rtnl group has listeners

From: Jamal Hadi Salim <jhs@...atatu.com>

As of today, rtnl code creates a new skb and unconditionally fills and
broadcasts it to the relevant group. For most operations this is okay
and doesn't waste resources in general.

When operations are done without the rtnl_lock, as in tc-flower, such
skb allocation, message fill and no-op broadcasting can happen in all
cores of the system, which contributes to system pressure and wastes
precious cpu cycles when no one will receive the built message.

Introduce this helper so rtnetlink operations can simply check if someone
is listening and then proceed if necessary.

Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
Signed-off-by: Victor Nogueira <victor@...atatu.com>
Signed-off-by: Pedro Tammela <pctammela@...atatu.com>
---
 include/linux/rtnetlink.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 3d6cf306cd55..a7d757e96c55 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -130,4 +130,11 @@ extern int ndo_dflt_bridge_getlink(struct sk_buff *skb, u32 pid, u32 seq,
 
 extern void rtnl_offload_xstats_notify(struct net_device *dev);
 
+static inline int rtnl_has_listeners(const struct net *net, u32 group)
+{
+	struct sock *rtnl = net->rtnl;
+
+	return netlink_has_listeners(rtnl, group);
+}
+
 #endif	/* __LINUX_RTNETLINK_H */
-- 
2.40.1