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

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Message-ID: <YFsVzP6P9l0aaIVo@unreal>
Date:   Wed, 24 Mar 2021 12:34:52 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Yejune Deng <yejune.deng@...il.com>
Cc:     davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, yejune@...il.com
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 <yejune.deng@...il.com>
> ---
>  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
>