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

[Leon Romanovsky]

On Wed, Mar 24, 2021 at 07:01:19PM +0800, Yejune Deng wrote:
> 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.

It is part of that cargo cult. Please support your claim with
performance numbers when this likely/unlikely will give any difference.

Thanks

> 
> On Wed, Mar 24, 2021 at 6:34 PM Leon Romanovsky  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 
> > > ---
> > >  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_gw4;
> > >   } else if (rt->rt_gw_family == AF_INET6) {
> > >   return __ipv6_confirm_neigh_stub(dev, >rt_gw6);
> > > --
> > > 2.29.0
> > >

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

[Yejune Deng]

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  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 
> > ---
> >  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_gw4;
> >   } else if (rt->rt_gw_family == AF_INET6) {
> >   return __ipv6_confirm_neigh_stub(dev, >rt_gw6);
> > --
> > 2.29.0
> >

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

[Leon Romanovsky]

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 
> ---
>  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_gw4;
>   } else if (rt->rt_gw_family == AF_INET6) {
>   return __ipv6_confirm_neigh_stub(dev, >rt_gw6);
> -- 
> 2.29.0
> 

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

[Yejune Deng]

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

Signed-off-by: Yejune Deng 
---
 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_gw4;
} else if (rt->rt_gw_family == AF_INET6) {
return __ipv6_confirm_neigh_stub(dev, >rt_gw6);
-- 
2.29.0