net: Remove likely from l3mdev_master_ifindex_by_index

JIRA: https://issues.redhat.com/browse/RHEL-84551
Upstream Status: linux.git

commit 9e542ff
Author: Breno Leitao <leitao@debian.org>
Date:   Tue Oct 8 09:32:04 2024 -0700

    net: Remove likely from l3mdev_master_ifindex_by_index

    The likely() annotation in l3mdev_master_ifindex_by_index() has been
    found to be incorrect 100% of the time in real-world workloads (e.g.,
    web servers).

    Annotated branches shows the following in these servers:

            correct incorrect  %        Function                  File              Line
                  0 169053813 100 l3mdev_master_ifindex_by_index l3mdev.h             81

    This is happening because l3mdev_master_ifindex_by_index() is called
    from __inet_check_established(), which calls
    l3mdev_master_ifindex_by_index() passing the socked bounded interface.

            l3mdev_master_ifindex_by_index(net, sk->sk_bound_dev_if);

    Since most sockets are not going to be bound to a network device,
    the likely() is giving the wrong assumption.

    Remove the likely() annotation to ensure more accurate branch
    prediction.

    Signed-off-by: Breno Leitao <leitao@debian.org>
    Reviewed-by: David Ahern <dsahern@kernel.org>
    Reviewed-by: Eric Dumazet <edumazet@google.com>
    Link: https://patch.msgid.link/20241008163205.3939629-1-leitao@debian.org
    Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Signed-off-by: Antoine Tenart <atenart@redhat.com>

Author: atenart

include/net/l3mdev.h

@@ -78,7 +78,7 @@ static inline int l3mdev_master_ifindex_by_index(struct net *net, int ifindex)
 	struct net_device *dev;
 	int rc = 0;
 
-	if (likely(ifindex)) {
+	if (ifindex) {
 		rcu_read_lock();
 
 		dev = dev_get_by_index_rcu(net, ifindex);