netdev - Re: [PATCH net-next 2/2] ipv6: fib6: avoid indirect calls from fib6_rule

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Date:   Mon, 22 Jun 2020 12:13:03 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Brian Vazquez <brianvv@...gle.com>,
        Brian Vazquez <brianvv.kernel@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Luigi Rizzo <lrizzo@...gle.com>
Subject: Re: [PATCH net-next 2/2] ipv6: fib6: avoid indirect calls from
 fib6_rule_lookup

Hi,

On Fri, 2020-06-19 at 20:14 -0700, Brian Vazquez wrote:
> @@ -111,11 +111,13 @@ struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
>  	} else {
>  		struct rt6_info *rt;
>  
> -		rt = lookup(net, net->ipv6.fib6_local_tbl, fl6, skb, flags);
> +		rt = pol_lookup_func(lookup,
> +			     net, net->ipv6.fib6_local_tbl, fl6, skb, flags);
>  		if (rt != net->ipv6.ip6_null_entry && rt->dst.error != -EAGAIN)
>  			return &rt->dst;
>  		ip6_rt_put_flags(rt, flags);
> -		rt = lookup(net, net->ipv6.fib6_main_tbl, fl6, skb, flags);
> +		rt = pol_lookup_func(lookup,
> +			     net, net->ipv6.fib6_main_tbl, fl6, skb, flags);
>  		if (rt->dst.error != -EAGAIN)
>  			return &rt->dst;
>  		ip6_rt_put_flags(rt, flags);

Have you considered instead factoring out the slice of
fib6_rule_lookup() using indirect calls to an header file? it looks
like here (gcc 10.1.1) it sufficent let the compiler use direct calls
and will avoid the additional branches.

Thanks!

Paolo