netdev - Re: [PATCH net-next] tcp: use RCU in __inet{6}_check

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Message-ID: <CAL+tcoBAVmTk_JBX=OEBqZZuoSzZd8bjuw9rgwRLMd9fvZOSkA@mail.gmail.com>
Date: Sun, 2 Mar 2025 17:48:59 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, Simon Horman <horms@...nel.org>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next] tcp: use RCU in __inet{6}_check_established()

On Sun, Mar 2, 2025 at 3:46 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> When __inet_hash_connect() has to try many 4-tuples before
> finding an available one, we see a high spinlock cost from
> __inet_check_established() and/or __inet6_check_established().
>
> This patch adds an RCU lookup to avoid the spinlock
> acquisition if the 4-tuple is found in the hash table.
>
> Note that there are still spin_lock_bh() calls in
> __inet_hash_connect() to protect inet_bind_hashbucket,
> this will be fixed in a future patch.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

After Eric just reminded me, I similarly conduct the test and succeed
to see a 7% performance increase. And there are 1225112852 times early
return with -EADDRNOTAVAIL (during single test period) in RCU
protection newly added in this patch, which means we save 1225112852
times using unnecessary spin lock. It's really remarkable!

So,
Tested-by: Jason Xing <kerneljasonxing@...il.com>
Reviewed-by: Jason Xing <kerneljasonxing@...il.com>

Thank you.