linux-kernel - Re: [PATCH v2 0/8] Asynchronous device/driver probing support

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Date:	Tue, 31 Mar 2015 16:39:49 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Luis R . Rodriguez" <mcgrof@...e.com>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Olof Johansson <olof@...om.net>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH v2 0/8] Asynchronous device/driver probing support

On Mon, Mar 30, 2015 at 04:20:02PM -0700, Dmitry Torokhov wrote:
> This series is a combination of changes proposed by Luis a couple months
> ago and implementation used by Chrome OS. The issue we are trying to solve
> here is "slow" devices and drivers spending "too much time" in their probe()
> methods and it affects:
> 
> - overall kernel boot process when drivers are compiled into the kernel
>   and slow devices stall entire boot progress;
> - systemd desire to time out module loading process.
> 
> Unlike Luis' proposal we do make use of asycn_schedule() infrastructure
> instead of using a dedicated workqueue, so all  existing synchronization
> points in kernel that wait for device registration still work the same.
> Also, the asynchronous probing is done not only during driver registration
> (i.e. when devices are probed asynchronously only if they are registered
> before the driver), but also during device registration and deferred probe
> handling. This way slow devices do not stall kernel boot even when drivers
> are compiled into the kernel.
> 
> The last patch is for adventurous people to try and force
> fully-asynchronous boot. It works for me with limited success - I can boot
> Rockhip-based box to userspace as long as I force serial to be sychronously
> probed and ignore the fact that most devices are using "dummy" regulators
> as regulator subsystem really expects regulators to be registered in
> orderly fashion on OF-based systems.
> 
> Changes from v1:
> 
> - Changed verbage in change logs and code to emphasise that
>   PROBE_PREFER_ASYNCHRONOUS is a temporary measure and the end goal is
>   to enable asynchronous probing by default, as requested by Tejun.

Looks good to me.  Please feel free to add

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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