Re: [PATCH net-next] net: Remove likely from l3mdev_master_ifindex_by_index

[Eric Dumazet]

On Tue, Oct 8, 2024 at 8:25 PM David Ahern <dsahern@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >  include/net/l3mdev.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
>
> Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>