linux-kernel - Re: Performance regression in ip_set

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Date: Wed, 10 Jan 2024 18:23:42 +0800
From: David Wang <00107082@....com>
To: ale.crismani@...omattic.com,
	kadlec@...filter.org,
	xiaolinkui@...inos.cn,
	pablo@...filter.org
Cc: linux-kernel@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: Performance regression in ip_set_swap on 6.1.69

I confirmed this on 6.7 that this was introduced by commit 28628fa952fefc7f2072ce6e8016968cc452b1ba with following changes:

	 static inline void
	@@ -1397,6 +1394,9 @@ static int ip_set_swap(struct sk_buff *skb, const struct nfnl_info *info,
		ip_set(inst, to_id) = from;
		write_unlock_bh(&ip_set_ref_lock);
	 
	+       /* Make sure all readers of the old set pointers are completed. */
	+       synchronize_rcu();
	+
		return 0;
	 }

synchronize_rcu causes the delay, and its usage here is very confusing, there is no reclaimer code after it.


FYI
David