netdev - Re: [PATCH net-next 0/4] net-sysfs: remove the rtnl_trylock/restart

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Message-ID: <173753699410.42919.17052319601873170277@kwain>
Date: Wed, 22 Jan 2025 10:09:54 +0100
From: Antoine Tenart <atenart@...nel.org>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com, stephen@...workplumber.org, gregkh@...uxfoundation.org, netdev@...r.kernel.org, Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH net-next 0/4] net-sysfs: remove the rtnl_trylock/restart_syscall construction

Quoting Maxime Chevallier (2025-01-22 09:50:24)
> On Fri, 17 Jan 2025 11:26:07 +0100
> Antoine Tenart <atenart@...nel.org> wrote:
> 
> > The series initially aimed at improving spins (and thus delays) while
> > accessing net sysfs under rtnl lock contention[1]. The culprit was the
> > trylock/restart_syscall constructions. There wasn't much interest at the
> > time but it got traction recently for other reasons (lowering the rtnl
> > lock pressure).
> > 
> > Since the RFC[1]:
> > 
> > - Limit the breaking of the sysfs protection to sysfs_rtnl_lock() only
> >   as this is not needed in the whole rtnl locking section thanks to the
> >   additional check on dev_isalive(). This simplifies error handling as
> >   well as the unlocking path.
> > - Used an interruptible version of rtnl_lock, as done by Jakub in
> >   his experiments.
> > - Removed a WARN_ONCE_ONCE call [Greg].
> > - Removed explicit inline markers [Stephen].
> > 
> > Most of the reasoning is explained in comments added in patch 1. This
> > was tested by stress-testing net sysfs attributes (read/write ops) while
> > adding/removing queues and adding/removing veths, all in parallel. I
> > also used an OCP single node cluster, spawning lots of pods.
> > 
> > Thanks,
> > Antoine
> > 
> > [1] https://lore.kernel.org/all/20231018154804.420823-1-atenart@kernel.org/T/
> 
> Thanks for that work, it looks like this would address this problem
> faced recently by Christophe (in CC) :
> 
> https://lore.kernel.org/netdev/d416a14ec38c7ba463341b83a7a9ec6ccc435246.1734419614.git.christophe.leroy@csgroup.eu/

That's likely given the diff, I actually wanted to Cc him here but looks
like I forgot... Thanks for doing so.