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

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Message-ID: <20250122095024.35c78381@device-291.home>
Date: Wed, 22 Jan 2025 09:50:24 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Antoine Tenart <atenart@...nel.org>
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

Hi Antoine,

On Fri, 17 Jan 2025 11:26:07 +0100
Antoine Tenart <atenart@...nel.org> wrote:

> Hi,
> 
> 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/

Thanks,

Maxime