linux-kernel - Re: [PATCH v3] net/bridge: Optimizing read-write locks in ebtables.c

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Message-ID: <20240924094054.2d005c76@fedora>
Date: Tue, 24 Sep 2024 09:40:54 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: yushengjin <yushengjin@...ontech.com>, pablo@...filter.org,
 kadlec@...filter.org, roopa@...dia.com, razor@...ckwall.org,
 davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 netfilter-devel@...r.kernel.org, coreteam@...filter.org,
 bridge@...ts.linux.dev, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] net/bridge: Optimizing read-write locks in
 ebtables.c

On Tue, 24 Sep 2024 15:46:17 +0200
Eric Dumazet <edumazet@...gle.com> wrote:

> On Tue, Sep 24, 2024 at 3:33 PM Stephen Hemminger
> <stephen@...workplumber.org> wrote:
> >
> > On Tue, 24 Sep 2024 17:09:06 +0800
> > yushengjin <yushengjin@...ontech.com> wrote:
> >  
> > > When conducting WRK testing, the CPU usage rate of the testing machine was
> > > 100%. forwarding through a bridge, if the network load is too high, it may
> > > cause abnormal load on the ebt_do_table of the kernel ebtable module, leading
> > > to excessive soft interrupts and sometimes even directly causing CPU soft
> > > deadlocks.
> > >
> > > After analysis, it was found that the code of ebtables had not been optimized
> > > for a long time, and the read-write locks inside still existed. However, other
> > > arp/ip/ip6 tables had already been optimized a lot, and performance bottlenecks
> > > in read-write locks had been discovered a long time ago.
> > >
> > > Ref link: https://lore.kernel.org/lkml/20090428092411.5331c4a1@nehalam/
> > >
> > > So I referred to arp/ip/ip6 modification methods to optimize the read-write
> > > lock in ebtables.c.  
> >
> > What about doing RCU instead, faster and safer.  
> 
> Safer ? How so ?
> 
> Stephen, we have used this stuff already in other netfilter components
> since 2011
> 
> No performance issue at all.
> 

I was thinking that lockdep and analysis tools do better job looking at RCU.
Most likely, the number of users of ebtables was small enough that nobody looked
hard at it until now.