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

From: Greg Kroah-Hartman
Date: Mon Apr 06 2015 - 13:45:38 EST


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@xxxxxxxxxx>
>
> Greg, it would be great if it could make it in 4.1.

It's on my list of patches to review next...

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