linux-kernel - Re: [PATCH v7 3/4] driver core: shut down devices asynchronously

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Message-ID: <20240627055515.GC15415@lst.de>
Date: Thu, 27 Jun 2024 07:55:15 +0200
From: Christoph Hellwig <hch@....de>
To: Stuart Hayes <stuart.w.hayes@...il.com>
Cc: linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Martin Belanger <Martin.Belanger@...l.com>,
	Oliver O'Halloran <oohall@...il.com>,
	Daniel Wagner <dwagner@...e.de>, Keith Busch <kbusch@...nel.org>,
	Lukas Wunner <lukas@...ner.de>, David Jeffery <djeffery@...hat.com>,
	Jeremy Allison <jallison@....com>, Jens Axboe <axboe@...com>,
	Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
	linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v7 3/4] driver core: shut down devices asynchronously

On Wed, Jun 26, 2024 at 02:46:49PM -0500, Stuart Hayes wrote:
> Add code to allow asynchronous shutdown of devices, ensuring that each
> device is shut down before its parents & suppliers.
> 
> Add async_shutdown_enable to struct device_driver, and expose it via sysfs.
> This can be used to view or change driver opt-in to asynchronous shutdown.
> Only devices with drivers that have async_shutdown_enable enabled will be
> shut down asynchronously.
> 
> This can dramatically reduce system shutdown/reboot time on systems that
> have multiple devices that take many seconds to shut down (like certain
> NVMe drives). On one system tested, the shutdown time went from 11 minutes
> without this patch to 55 seconds with the patch.

We discussed this before, but there is no summary of it and I of course
forgot the conclusion:

 - why don't we do this by default?
 - why is it safe to user enable it?

> + * @shutdown_after - used during device shutdown to ensure correct shutdown ordering.

Overly long line.

> +static ssize_t async_shutdown_enable_store(struct device_driver *drv, const char *buf,

.. and here.