linux-kernel - Re: [PATCH 1/3] Revert "netfilter: x_tables: Update remaining dereference to RCU"

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Message-ID: <20210304074337.GH17911@breakpoint.cc>
Date:   Thu, 4 Mar 2021 08:43:37 +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 1/3] Revert "netfilter: x_tables: Update remaining
 dereference to RCU"

Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz> wrote:
> This reverts commit 443d6e86f821a165fae3fc3fc13086d27ac140b1.
> 
> This (and the following) 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.
> 
> See https://lore.kernel.org/patchwork/patch/151796/ for why using RCU is
> not a good idea.

Please don't add links for the rationale.