Re: [PATCH v6 3/4] driver core: shut down devices asynchronously

[Keith Busch <kbusch@kernel.org>]

On Thu, May 16, 2024 at 10:49:19AM -0500, Stuart Hayes wrote:
> Add code to shut down devices asynchronously, while ensuring that each
> device is shut down before its parents & suppliers, and allowing devices
> that share a driver to be shutdown one at a time if necessary.
> 
> Add /sys/kernel/async_shutdown to allow user control of this feature:
> 
>   safe: shut down all devices synchronously, unless driver prefers async
> 	shutdown (driver opt-in) (default)
>   on:	shut down all devices asynchronously, unless disabled by the driver
> 	(driver opt-out)
>   off:	shut down all devices synchronously
> 
> Add async_shutdown to struct device_driver, and expose it via sysfs.
> This will be used to view or change driver opt-in/opt-out of asynchronous
> shutdown, if it is globally enabled.
> 
>  async:   driver opt-in to async device shutdown (devices will be shut down
>           asynchronously if async_shutdown is "on" or "safe")
>  sync:    driver opt-out of async device shutdown (devices will always be
>           shut down synchronously)
>  default: devices will be shutdown asynchronously if async_shutdown is "on"
> 
> 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.

I've successfully tested this out on a few systems, and noticing a very
decent shutdown time on my nvme systems. I also like the current
solution here, as the two-pass method was harder to follow.

So I think just remove the extra options that Christoph mentioned and
always use the driver's preferred shutdown method, then this would all
look good to me.