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>

diff --git a/include/net/l3mdev.h b/include/net/l3mdev.h
index 031c661aa14df7148c51f54284ab6e33429352d6..2d6141f28b53097fe452cbdaf5faa977fc6e6782 100644 (file)
--- a/include/net/l3mdev.h
+++ b/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);