Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756032AbbGEJEF (ORCPT ); Sun, 5 Jul 2015 05:04:05 -0400 Received: from mail-ig0-f175.google.com ([209.85.213.175]:37771 "EHLO mail-ig0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755930AbbGEJEC (ORCPT ); Sun, 5 Jul 2015 05:04:02 -0400 MIME-Version: 1.0 Date: Sat, 4 Jul 2015 07:09:19 -0700 X-Google-Sender-Auth: 5cHnmP41ey4rKvcdRgpWgjSGbls Message-ID: Subject: Re: [PATCH 2/8] driver-core: add asynchronous probing support for drivers From: Dan Williams To: "Luis R. Rodriguez" Cc: Tom Gundersen , Dmitry Torokhov , Greg Kroah-Hartman , Tejun Heo , Linux Kernel Mailing List , Arjan van de Ven , Rusty Russell , Olof Johansson , Tetsuo Handa Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3924 Lines: 85 On Fri, Jul 3, 2015 at 11:30 AM, Luis R. Rodriguez 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 >> 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" >> > >> > >> > Signed-off-by: Dmitry Torokhov >> > --- >> > 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/