Re: [PATCH v2 net-next] tcp: improve inet6_ehashfn() entropy

[Simon Horman <horms@kernel.org>]

On Fri, Mar 13, 2026 at 12:03:46PM +0000, Eric Dumazet wrote:
> 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 beter 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>
> ---
> v2: do not include @lport in the jhash computation.
>     Add a comment explaining why we need @lport being added.

Reviewed-by: Simon Horman <horms@kernel.org>