linux-kernel - Re: [PATCH 2/3] Revert "netfilter: x_tables: Switch synchronization to RCU"

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Date:   Thu, 4 Mar 2021 08:44:52 +0100
From:   Florian Westphal <fw@...len.de>
To:     Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>
Cc:     pablo@...filter.org, kadlec@...filter.org, fw@...len.de,
        netfilter-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] Revert "netfilter: x_tables: Switch synchronization
 to RCU"

Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz> wrote:
> This reverts commit cc00bcaa589914096edef7fb87ca5cee4a166b5c.
> 
> This (and the preceding) patch basically re-implemented the RCU
> mechanisms of patch 784544739a25. That patch was replaced because of the
> performance problems that it created when replacing tables. Now, we have
> the same issue: the call to synchronize_rcu() makes replacing tables
> slower by as much as an order of magnitude.

Can you give roigh numbers?

> See https://lore.kernel.org/patchwork/patch/151796/ for why using RCU is
> not a good idea.

Please, no link.