superrob1500
/
mirror-linux
mirror of https://github.com/torvalds/linux
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

tcp: improve inet6_ehashfn() entropy 

Instead of only using the 32 low order bits of the local address,
use all of them.

Xor net_hash_mix(net) with the 32 high order bits of the local address
so that we can use __jhash_mix() three times.

If we were hashing 4 extra bytes, we would need one __jhash_final()
which is a bit expensive.

Using net_hash_mix() at the beginning allows better register allocation.

We no longer use a cascade of two jhash and inet6_ehash_secret,
this was dubious/weak.

Add a comment explaining why @lport is not part of the jhash computation.

$ scripts/bloat-o-meter -t vmlinux.0 vmlinux.1
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-24 (-24)
Function                                     old     new   delta
inet6_ehashfn                                330     306     -24
Total: Before=24855958, After=24855934, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260313120346.3378811-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
master
Eric Dumazet 2026-03-13 12:03:46 +00:00 committed by Jakub Kicinski
parent 6a33a70626
commit 854587e69e
1 changed files with 35 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
net/ipv6/inet6_hashtables.c
View File

@ -35,13 +35,43 @@ u32 inet6_ehashfn(const struct net *net,
const struct in6_addr *laddr, const u16 lport,
const struct in6_addr *faddr, const __be16 fport)
{
u32 lhash, fhash;
u32 a, b, c;
lhash = (__force u32)laddr->s6_addr32[3];
fhash = __ipv6_addr_jhash(faddr, tcp_ipv6_hash_secret);
/*
* Please look at jhash() implementation for reference.
* Hash laddr + faddr + lport/fport + net_hash_mix.
* Notes:
* We combine laddr[0] (high order 32 bits of local address)
* with net_hash_mix() to avoid using __jhash_final(a, b, c).
*
* We do not include JHASH_INITVAL + 36 contribution
* to initial values of a, b, c.
*/
return lport + __inet6_ehashfn(lhash, 0, fhash, fport,
inet6_ehash_secret + net_hash_mix(net));
a = b = c = tcp_ipv6_hash_secret;
a += (__force u32)laddr->s6_addr32[0] ^ net_hash_mix(net);
b += (__force u32)laddr->s6_addr32[1];
c += (__force u32)laddr->s6_addr32[2];
__jhash_mix(a, b, c);
a += (__force u32)laddr->s6_addr32[3];
b += (__force u32)faddr->s6_addr32[0];
c += (__force u32)faddr->s6_addr32[1];
__jhash_mix(a, b, c);
a += (__force u32)faddr->s6_addr32[2];
b += (__force u32)faddr->s6_addr32[3];
c += (__force u32)fport;
__jhash_mix(a, b, c);
/* Note: We need to add @lport instead of fully hashing it.
* See commits 9544d60a2605 ("inet: change lport contribution
* to inet_ehashfn() and inet6_ehashfn()") and d4438ce68bf1
* ("inet: call inet6_ehashfn() once from inet6_hash_connect()")
* for references.
*/
return lport + c;
}
EXPORT_SYMBOL_GPL(inet6_ehashfn);