netdev - Re: [PATCH net-next-2.6 v2] filter: optimize sk_run

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Date:	Fri, 19 Nov 2010 23:17:18 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	eric.dumazet@...il.com, xiaosuo@...il.com
Cc:	davem@...emloft.net, hagen@...u.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next-2.6 v2] filter: optimize sk_run_filter

Just my thought again...

Eric Dumazet wrote:
> @@ -167,34 +168,36 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int
>  	unsigned long memvalid = 0;
>  	u32 tmp;
>  	int k;

Is this 'k' useful?

> -	int pc;
>  
>  	BUILD_BUG_ON(BPF_MEMWORDS > BITS_PER_LONG);
>  	/*
>  	 * Process array of filter instructions.
>  	 */
> -	for (pc = 0; pc < flen; pc++) {
> -		const struct sock_filter *fentry = &filter[pc];
> -		u32 f_k = fentry->k;
> +	for (;; fentry++) {
> +#if defined(CONFIG_X86_32)
> +#define	K (fentry->k)
> +#else
> +		const u32 K = fentry->k;

What happens if we use

	u32 f_k = fentry->k;

and

>  		case BPF_S_LD_W_ABS:
> -			k = f_k;
> +			k = K;

remove this assignment and

>  load_w:
>  			ptr = load_pointer(skb, k, 4, &tmp);

change to

	ptr = load_pointer(skb, (int) f_k, 4, &tmp);

and

>  		case BPF_S_LD_W_IND:
> -			k = X + f_k;
> +			k = X + K;

change to

	f_k += X;

?
>  			goto load_w;
--
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