Re: [PATCH net-next 2/2] inet: call inet6_ehashfn() once from inet6_hash_connect()

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Eric Dumazet <edumazet@google.com>
Date: Wed,  5 Mar 2025 03:45:50 +0000
> inet6_ehashfn() being called from __inet6_check_established()
> has a big impact on performance, as shown in the Tested section.
> 
> After prior patch, we can compute the hash for port 0
> from inet6_hash_connect(), and derive each hash in
> __inet_hash_connect() from this initial hash:
> 
> hash(saddr, lport, daddr, dport) == hash(saddr, 0, daddr, dport) + lport
> 
> Apply the same principle for __inet_check_established(),
> although inet_ehashfn() has a smaller cost.
> 
> Tested:
> 
> Server: ulimit -n 40000; neper/tcp_crr -T 200 -F 30000 -6 --nolog
> Client: ulimit -n 40000; neper/tcp_crr -T 200 -F 30000 -6 --nolog -c -H server
> 
> Before this patch:
> 
>   utime_start=0.286131
>   utime_end=4.378886
>   stime_start=11.952556
>   stime_end=1991.655533
>   num_transactions=1446830
>   latency_min=0.001061085
>   latency_max=12.075275028
>   latency_mean=0.376375302
>   latency_stddev=1.361969596
>   num_samples=306383
>   throughput=151866.56
> 
> perf top:
> 
>  50.01%  [kernel]       [k] __inet6_check_established
>  20.65%  [kernel]       [k] __inet_hash_connect
>  15.81%  [kernel]       [k] inet6_ehashfn
>   2.92%  [kernel]       [k] rcu_all_qs
>   2.34%  [kernel]       [k] __cond_resched
>   0.50%  [kernel]       [k] _raw_spin_lock
>   0.34%  [kernel]       [k] sched_balance_trigger
>   0.24%  [kernel]       [k] queued_spin_lock_slowpath
> 
> After this patch:
> 
>   utime_start=0.315047
>   utime_end=9.257617
>   stime_start=7.041489
>   stime_end=1923.688387
>   num_transactions=3057968
>   latency_min=0.003041375
>   latency_max=7.056589232
>   latency_mean=0.141075048    # Better latency metrics
>   latency_stddev=0.526900516
>   num_samples=312996
>   throughput=320677.21        # 111 % increase, and 229 % for the series
> 
> perf top: inet6_ehashfn is no longer seen.
> 
>  39.67%  [kernel]       [k] __inet_hash_connect
>  37.06%  [kernel]       [k] __inet6_check_established
>   4.79%  [kernel]       [k] rcu_all_qs
>   3.82%  [kernel]       [k] __cond_resched
>   1.76%  [kernel]       [k] sched_balance_domains
>   0.82%  [kernel]       [k] _raw_spin_lock
>   0.81%  [kernel]       [k] sched_balance_rq
>   0.81%  [kernel]       [k] sched_balance_trigger
>   0.76%  [kernel]       [k] queued_spin_lock_slowpath
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Interesting optimisation, thanks!