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Commit ddc214c4 authored by Eric Dumazet's avatar Eric Dumazet Committed by Patrick McHardy
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netfilter: arp_tables: unfold two critical loops in arp_packet_match() 



x86 and powerpc can perform long word accesses in an efficient maner.
We can use this to unroll two loops in arp_packet_match(), to
perform arithmetic on long words instead of bytes. This is a win
on x86_64 for example.

Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: default avatarPatrick McHardy <kaber@trash.net>
parent 55df4ac0

net/ipv4/netfilter/arp_tables.c

+34 −10
Original line number Diff line number Diff line
@@ -73,6 +73,36 @@ static inline int arp_devaddr_compare(const struct arpt_devaddr_info *ap, 
	return (ret != 0);

}



/*

 * Unfortunatly, _b and _mask are not aligned to an int (or long int)

 * Some arches dont care, unrolling the loop is a win on them.

 */

static unsigned long ifname_compare(const char *_a, const char *_b, const char *_mask)

{

#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

	const unsigned long *a = (const unsigned long *)_a;

	const unsigned long *b = (const unsigned long *)_b;

	const unsigned long *mask = (const unsigned long *)_mask;

	unsigned long ret;



	ret = (a[0] ^ b[0]) & mask[0];

	if (IFNAMSIZ > sizeof(unsigned long))

		ret |= (a[1] ^ b[1]) & mask[1];

	if (IFNAMSIZ > 2 * sizeof(unsigned long))

		ret |= (a[2] ^ b[2]) & mask[2];

	if (IFNAMSIZ > 3 * sizeof(unsigned long))

		ret |= (a[3] ^ b[3]) & mask[3];

	BUILD_BUG_ON(IFNAMSIZ > 4 * sizeof(unsigned long));

#else

	unsigned long ret = 0;

	int i;



	for (i = 0; i < IFNAMSIZ; i++)

		ret |= (_a[i] ^ _b[i]) & _mask[i];

#endif

	return ret;

}



/* Returns whether packet matches rule or not. */

static inline int arp_packet_match(const struct arphdr *arphdr,

				   struct net_device *dev,
@@ -83,7 +113,7 @@ static inline int arp_packet_match(const struct arphdr *arphdr, 
	const char *arpptr = (char *)(arphdr + 1);

	const char *src_devaddr, *tgt_devaddr;

	__be32 src_ipaddr, tgt_ipaddr;

	int i, ret;

	long ret;



#define FWINV(bool, invflg) ((bool) ^ !!(arpinfo->invflags & (invflg)))
@@ -156,10 +186,7 @@ static inline int arp_packet_match(const struct arphdr *arphdr, 
	}



	/* Look for ifname matches.  */

	for (i = 0, ret = 0; i < IFNAMSIZ; i++) {

		ret |= (indev[i] ^ arpinfo->iniface[i])

			& arpinfo->iniface_mask[i];

	}

	ret = ifname_compare(indev, arpinfo->iniface, arpinfo->iniface_mask);



	if (FWINV(ret != 0, ARPT_INV_VIA_IN)) {

		dprintf("VIA in mismatch (%s vs %s).%s\n",
@@ -168,10 +195,7 @@ static inline int arp_packet_match(const struct arphdr *arphdr, 
		return 0;

	}



	for (i = 0, ret = 0; i < IFNAMSIZ; i++) {

		ret |= (outdev[i] ^ arpinfo->outiface[i])

			& arpinfo->outiface_mask[i];

	}

	ret = ifname_compare(outdev, arpinfo->outiface, arpinfo->outiface_mask);



	if (FWINV(ret != 0, ARPT_INV_VIA_OUT)) {

		dprintf("VIA out mismatch (%s vs %s).%s\n",
@@ -221,7 +245,7 @@ unsigned int arpt_do_table(struct sk_buff *skb, 
			   const struct net_device *out,

			   struct xt_table *table)

{

	static const char nulldevname[IFNAMSIZ];

	static const char nulldevname[IFNAMSIZ] __attribute__((aligned(sizeof(long))));

	unsigned int verdict = NF_DROP;

	const struct arphdr *arp;

	bool hotdrop = false;