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

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Date:	Mon, 18 May 2015 14:48:19 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Tejun Heo <tj@...nel.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, Apr 06, 2015 at 07:45:30PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Apr 06, 2015 at 09:22:51AM -0700, Dmitry Torokhov wrote:
> > On Tue, Mar 31, 2015 at 04:39:49PM -0400, Tejun Heo wrote:
> > > 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>
> > 
> > Greg, it would be great if it could make it in 4.1.
> 
> It's on my list of patches to review next...

Greg, could we make 4.2 please? ;)

Thanks.

-- 
Dmitry
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