On Fri, Jul 3, 2015 at 11:30 AM, Luis R. Rodriguez <mcg...@suse.com> wrote: > On Sat, Jun 27, 2015 at 04:45:25PM -0700, Dan Williams wrote: >> On Mon, Mar 30, 2015 at 4:20 PM, Dmitry Torokhov >> <dmitry.torok...@gmail.com> wrote: >> > Some devices take a long time when initializing, and not all drivers are >> > suited to initialize their devices when they are open. For example, >> > input drivers need to interrogate their devices in order to publish >> > device's capabilities before userspace will open them. When such drivers >> > are compiled into kernel they may stall entire kernel initialization. >> > >> > This change allows drivers request for their probe functions to be >> > called asynchronously during driver and device registration (manual >> > binding is still synchronous). Because async_schedule is used to perform >> > asynchronous calls module loading will still wait for the probing to >> > complete. >> > >> > Note that the end goal is to make the probing asynchronous by default, >> > so annotating drivers with PROBE_PREFER_ASYNCHRONOUS is a temporary >> > measure that allows us to speed up boot process while we validating and >> > fixing the rest of the drivers and preparing userspace. >> > >> > This change is based on earlier patch by "Luis R. Rodriguez" >> > <mcg...@suse.com> >> > >> > Signed-off-by: Dmitry Torokhov <dmitry.torok...@gmail.com> >> > --- >> > drivers/base/base.h | 1 + >> > drivers/base/bus.c | 31 +++++++--- >> > drivers/base/dd.c | 149 >> > ++++++++++++++++++++++++++++++++++++++++++------- >> > include/linux/device.h | 28 ++++++++++ >> > 4 files changed, 182 insertions(+), 27 deletions(-) >> >> Just noticed this patch. It caught my eye because I had a hard time >> getting an open coded implementation of asynchronous probing to work >> in the new libnvdimm subsystem. Especially the messy races of tearing >> things down while probing is still in flight. I ended up implementing >> asynchronous device registration which eliminated a lot of complexity >> and of course the bugs. In general I tend to think that async >> registration is less risky than async probe since it keeps wider >> portions of the traditional device model synchronous > > but its not see -DEFER_PROBE even before async probe.
Except in that case you know probe has been seen by the driver at least once. So I see that as less of a surprise, but point taken. >> and leverages the >> fact that the device model is already well prepared for asynchronous >> arrival of devices due to hotplug. > > I think this sounds reasonable, do you have your code upstream or posted? Yes, see nd_device_register() in drivers/nvdimm/bus.c > If not will you be at Plumbers? Yes. > Maybe we shoudl talk about this as although > ChromeOS already likely already jumped on async probe we should address a > way forward and path forward for other distributions and I don't think anyone > is looking too much into it. async probe came to Linux for two reasons: > > * chromeos wanting it > * an incorrect systemd assumption on how the driver core works > > So long term we still need to address the systemd approach, are they going > to be defaulting now to async probe for all modules? How about for built-ins? > > We should talk about this and maybe at plumbers. > >> Splitting the "initial probe" from >> the "manual probe" case seems like a recipe for confusion. > > If you can come up with pros / cons on both strategies it'd be > valuable. The problem I ran into was needing to remove devices that still had yet to be probed and not being able to use registration completion vs the device_lock() to effectively synchronize the sub-system. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/