2018-10-12 12:25:24

by Michal Kubecek

Subject: [PATCH ipsec-next] xfrm: use complete IPv6 addresses for hash

In some environments it is common that many hosts share the same lower half
of their IPv6 addresses (in particular ::1). As __xfrm6_addr_hash() and
__xfrm6_daddr_saddr_hash() calculate the hash only from the lower halves,
as much as 1/3 of the hosts ends up in one hashtable chain which harms the
performance.

Use complete IPv6 addresses when calculating the hashes. Rather than just
adding two more words to the xor, use jhash2() for consistency with
__xfrm6_pref_hash() and __xfrm6_dpref_spref_hash().

Signed-off-by: Michal Kubecek <[email protected]>
---
net/xfrm/xfrm_hash.h | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/xfrm/xfrm_hash.h b/net/xfrm/xfrm_hash.h
index 61be810389d8..ce66323102f9 100644
--- a/net/xfrm/xfrm_hash.h
+++ b/net/xfrm/xfrm_hash.h
@@ -13,7 +13,7 @@ static inline unsigned int __xfrm4_addr_hash(const xfrm_address_t *addr)

static inline unsigned int __xfrm6_addr_hash(const xfrm_address_t *addr)
{
- return ntohl(addr->a6[2] ^ addr->a6[3]);
+ return jhash2((__force u32 *)addr->a6, 4, 0);
}

static inline unsigned int __xfrm4_daddr_saddr_hash(const xfrm_address_t *daddr,
@@ -26,8 +26,7 @@ static inline unsigned int __xfrm4_daddr_saddr_hash(const xfrm_address_t *daddr,
static inline unsigned int __xfrm6_daddr_saddr_hash(const xfrm_address_t *daddr,
const xfrm_address_t *saddr)
{
- return ntohl(daddr->a6[2] ^ daddr->a6[3] ^
- saddr->a6[2] ^ saddr->a6[3]);
+ return __xfrm6_addr_hash(daddr) ^ __xfrm6_addr_hash(saddr);
}

static inline u32 __bits2mask32(__u8 bits)
--
2.19.1

2018-10-16 08:39:32

by Steffen Klassert

Subject: Re: [PATCH ipsec-next] xfrm: use complete IPv6 addresses for hash

On Fri, Oct 12, 2018 at 02:24:44PM +0200, Michal Kubecek wrote:
> In some environments it is common that many hosts share the same lower half
> of their IPv6 addresses (in particular ::1). As __xfrm6_addr_hash() and
> __xfrm6_daddr_saddr_hash() calculate the hash only from the lower halves,
> as much as 1/3 of the hosts ends up in one hashtable chain which harms the
> performance.
>
> Use complete IPv6 addresses when calculating the hashes. Rather than just
> adding two more words to the xor, use jhash2() for consistency with
> __xfrm6_pref_hash() and __xfrm6_dpref_spref_hash().
>
> Signed-off-by: Michal Kubecek <[email protected]>

Applied to ipsec-next, thanks a lot!