netdev - Re: [PATCH net-next v2 1/3] net/sched: add retpoline wrapper for tc

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Message-ID: <20221130211643.01d65f46@kernel.org>
Date:   Wed, 30 Nov 2022 21:16:43 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Pedro Tammela <pctammela@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, kuniyu@...zon.com,
        Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH net-next v2 1/3] net/sched: add retpoline wrapper for tc

On Mon, 28 Nov 2022 12:44:54 -0300 Pedro Tammela wrote:
> On kernels compiled with CONFIG_RETPOLINE and CONFIG_NET_TC_INDIRECT_WRAPPER,
> optimize actions and filters that are compiled as built-ins into a direct call.
> The calls are ordered alphabetically, but new ones should be ideally
> added last.
> 
> On subsequent patches we expose the classifiers and actions functions
> and wire up the wrapper into tc.

> +#if IS_ENABLED(CONFIG_RETPOLINE) && IS_ENABLED(CONFIG_NET_TC_INDIRECT_WRAPPER)

The latter 'depends on' former, so just check the latter.

> +static inline int __tc_act(struct sk_buff *skb, const struct tc_action *a,
> +			   struct tcf_result *res)
> +{
> +	if (0) { /* noop */ }
> +#if IS_BUILTIN(CONFIG_NET_ACT_BPF)
> +	else if (a->ops->act == tcf_bpf_act)
> +		return tcf_bpf_act(skb, a, res);
> +#endif

How does the 'else if' ladder compare to a switch statement?

> +#ifdef CONFIG_NET_CLS_ACT
> +static inline int __tc_act(struct sk_buff *skb, const struct tc_action *a,
> +			   struct tcf_result *res)
> +{
> +	return a->ops->act(skb, a, res);
> +}
> +#endif
> +
> +#ifdef CONFIG_NET_CLS
> +static inline int __tc_classify(struct sk_buff *skb, const struct tcf_proto *tp,
> +				struct tcf_result *res)
> +{
> +	return tp->classify(skb, tp, res);
> +}
> +#endif

please don't wrap the static inline helpers in #ifdefs unless it's
actually necessary for build to pass.