2021-03-24 22:12:27

by Yejune Deng

Subject: [PATCH 1/2] net: ipv4: route.c: add likely() statements

Add likely() statements in ipv4_confirm_neigh() for 'rt->rt_gw_family
== AF_INET'.

Signed-off-by: Yejune Deng <[email protected]>
---
net/ipv4/route.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index fa68c2612252..5762d9bc671c 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -440,7 +440,7 @@ static void ipv4_confirm_neigh(const struct dst_entry *dst, const void *daddr)
struct net_device *dev = dst->dev;
const __be32 *pkey = daddr;

- if (rt->rt_gw_family == AF_INET) {
+ if (likely(rt->rt_gw_family == AF_INET)) {
pkey = (const __be32 *)&rt->rt_gw4;
} else if (rt->rt_gw_family == AF_INET6) {
return __ipv6_confirm_neigh_stub(dev, &rt->rt_gw6);
--
2.29.0

2021-03-25 02:51:39

by Leon Romanovsky

Subject: Re: [PATCH 1/2] net: ipv4: route.c: add likely() statements

On Wed, Mar 24, 2021 at 11:09:22AM +0800, Yejune Deng wrote:
> Add likely() statements in ipv4_confirm_neigh() for 'rt->rt_gw_family
> == AF_INET'.

Why? Such macros are beneficial in only specific cases, most of the time,
likely/unlikely is cargo cult.

>
> Signed-off-by: Yejune Deng <[email protected]>
> ---
> net/ipv4/route.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index fa68c2612252..5762d9bc671c 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -440,7 +440,7 @@ static void ipv4_confirm_neigh(const struct dst_entry *dst, const void *daddr)
> struct net_device *dev = dst->dev;
> const __be32 *pkey = daddr;
>
> - if (rt->rt_gw_family == AF_INET) {
> + if (likely(rt->rt_gw_family == AF_INET)) {
> pkey = (const __be32 *)&rt->rt_gw4;
> } else if (rt->rt_gw_family == AF_INET6) {
> return __ipv6_confirm_neigh_stub(dev, &rt->rt_gw6);
> --
> 2.29.0
>

2021-03-25 02:54:38

by Yejune Deng

Subject: Re: [PATCH 1/2] net: ipv4: route.c: add likely() statements

My reasons are as following: ipv4_confirm_neigh() belongs to
ipv4_dst_ops that family is AF_INET, and ipv4_neigh_lookup() is also
added likely() when rt->rt_gw_family is equal to AF_INET.

On Wed, Mar 24, 2021 at 6:34 PM Leon Romanovsky <[email protected]> wrote:
>
> On Wed, Mar 24, 2021 at 11:09:22AM +0800, Yejune Deng wrote:
> > Add likely() statements in ipv4_confirm_neigh() for 'rt->rt_gw_family
> > == AF_INET'.
>
> Why? Such macros are beneficial in only specific cases, most of the time,
> likely/unlikely is cargo cult.
>
> >
> > Signed-off-by: Yejune Deng <[email protected]>
> > ---
> > net/ipv4/route.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> > index fa68c2612252..5762d9bc671c 100644
> > --- a/net/ipv4/route.c
> > +++ b/net/ipv4/route.c
> > @@ -440,7 +440,7 @@ static void ipv4_confirm_neigh(const struct dst_entry *dst, const void *daddr)
> > struct net_device *dev = dst->dev;
> > const __be32 *pkey = daddr;
> >
> > - if (rt->rt_gw_family == AF_INET) {
> > + if (likely(rt->rt_gw_family == AF_INET)) {
> > pkey = (const __be32 *)&rt->rt_gw4;
> > } else if (rt->rt_gw_family == AF_INET6) {
> > return __ipv6_confirm_neigh_stub(dev, &rt->rt_gw6);
> > --
> > 2.29.0
> >