netdev - [PATCH net-next] sock: avoid dirtying incoming

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <a5af66d2a71c1fe229bbeee40db4a9aa48dd969a.1498038209.git.pabeni@redhat.com>
Date:   Wed, 21 Jun 2017 11:45:31 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] sock: avoid dirtying incoming_cpu if not needed

for connected socket, the incoming_cpu field in the sock struct
is not going to change frequently, but we are setting it
unconditionally for each packet.

Since sk_incoming_cpu and sk_flags share the same cacheline,
and the latter is access by udp_recvmsg(), this cause a cache
miss for each packet for UDP connected socket.

With this patch, we set the incoming cpu field only when the
ingress cpu really changes.

This gives a small but measurable performance improvement for
connected UDP socket.

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 include/net/sock.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 858891c..00d0914 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -907,7 +907,10 @@ static inline int sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)

 static inline void sk_incoming_cpu_update(struct sock *sk)
 {
-	sk->sk_incoming_cpu = raw_smp_processor_id();
+	int cpu = raw_smp_processor_id();
+
+	if (unlikely(sk->sk_incoming_cpu != cpu))
+		sk->sk_incoming_cpu = cpu;
 }

 static inline void sock_rps_record_flow_hash(__u32 hash)
-- 
2.9.4