| Message ID | 20241008163205.3939629-1-leitao@debian.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 9e542ff8b79ae1871074d3a7dca7de9e7374eeda |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next] net: Remove likely from l3mdev_master_ifindex_by_index | expand |
On 10/8/24 10:32 AM, Breno Leitao wrote: > 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> > --- > include/net/l3mdev.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > Reviewed-by: David Ahern <dsahern@kernel.org>
On Tue, Oct 8, 2024 at 8:25 PM David Ahern <dsahern@kernel.org> wrote: > > On 10/8/24 10:32 AM, Breno Leitao wrote: > > 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> > > --- > > include/net/l3mdev.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > Reviewed-by: David Ahern <dsahern@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com>
Hello: This patch was applied to netdev/net-next.git (main) by Paolo Abeni <pabeni@redhat.com>: On Tue, 8 Oct 2024 09:32:04 -0700 you wrote: > 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 > > [...] Here is the summary with links: - [net-next] net: Remove likely from l3mdev_master_ifindex_by_index https://git.kernel.org/netdev/net-next/c/9e542ff8b79a You are awesome, thank you!
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);
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> --- include/net/l3mdev.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)