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[2a03:2880:30ff:9::face:b00c]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c8e05a7e87sm4428868a12.24.2024.10.08.09.32.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2024 09:32:28 -0700 (PDT) From: Breno Leitao To: David Ahern , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: kernel-team@meta.com, netdev@vger.kernel.org (open list:L3MDEV), linux-kernel@vger.kernel.org (open list) Subject: [PATCH net-next] net: Remove likely from l3mdev_master_ifindex_by_index Date: Tue, 8 Oct 2024 09:32:04 -0700 Message-ID: <20241008163205.3939629-1-leitao@debian.org> X-Mailer: git-send-email 2.43.5 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org 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 Reviewed-by: David Ahern Reviewed-by: Eric Dumazet --- include/net/l3mdev.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/net/l3mdev.h b/include/net/l3mdev.h index 031c661aa14d..2d6141f28b53 100644 --- 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);