From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755698AbaIDVV0 (ORCPT ); Thu, 4 Sep 2014 17:21:26 -0400 Received: from cantor2.suse.de ([195.135.220.15]:38092 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755594AbaIDVVX (ORCPT ); Thu, 4 Sep 2014 17:21:23 -0400 Date: Thu, 4 Sep 2014 23:21:18 +0200 From: "Luis R. Rodriguez" To: Greg KH Cc: Dmitry Torokhov , Arjan van de Ven , "Luis R. Rodriguez" , falcon@meizu.com, tiwai@suse.de, tj@kernel.org, linux-kernel@vger.kernel.org, oleg@redhat.com, akpm@linux-foundation.org, penguin-kernel@i-love.sakura.ne.jp, joseph.salisbury@canonical.com, bpoirier@suse.de, Mel Gorman Subject: Re: [RFC v1 0/3] driver-core: add asynch module loading support Message-ID: <20140904212118.GB3347@wotan.suse.de> References: <1409475800-17573-1-git-send-email-mcgrof@do-not-panic.com> <540334B2.7000009@linux.intel.com> <20140831175040.GA17827@core.coreip.homeip.net> <5403767E.1020107@linux.intel.com> <20140831193140.GA12678@kroah.com> <20140831201407.GB19881@core.coreip.homeip.net> <20140831204035.GA4793@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140831204035.GA4793@kroah.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 31, 2014 at 01:40:35PM -0700, Greg KH wrote: > On Sun, Aug 31, 2014 at 01:14:07PM -0700, Dmitry Torokhov wrote: > > On Sun, Aug 31, 2014 at 12:31:40PM -0700, Greg KH wrote: > > > On Sun, Aug 31, 2014 at 12:24:46PM -0700, Arjan van de Ven wrote: > > > > >>before we added the current async approach the approach of async init calls was tried > > > > >>At the time, Linus hated it and he was right, it was not the right thing. > > > > >> > > > > >>What is different this time to make this the right thing to do ? > > > > > > > > > >Because otherwise drivers still have to do this, but open code it. Let's say I > > > > >have a long operations (i.e. for some touchpads it takes about 2 secs to reset > > > > >and configure it). I can offload that part into async_schedule() so it does not > > > > >stop initialization of the rest of the system (why would I want to delay > > > > >initializing of USB or storage system until touchpad is ready?) but if that > > > > >initialization fails we end up with partially bound driver and device that is > > > > >not really operable. I would very much prefer async and sync cases be the same > > > > >- if probe() fails the driver is not bound to the device. > > > > > > > > > >I think it is wrong to make async probing system-wide, but driver opt-in shoudl > > > > >be fine and right thing to do. > > > > > > > > > > > > > I am completely fine if we make basically an async wrapper for > > > > pci_register_driver() and friends.. that would be convenient I suppose. > > > > > > > > (but then again, in reality very few drivers take real time to init... most already > > > > do the heavy work in open(). Not all can, sure, but if you look at a bootgraph.pl > > > > graph of a typical boot it's only a few that matter). > > > > Input devices normally can't as we need to publish their capabilities before > > users start opening them. > > > > > > And many drivers need to register with a subsystem, and there's some ordering around that, > > > > and that's why we ended up with the async cookie stuff, so that you can do the > > > > heavy work in parallel, but order near the end at registeration-with-the-subsystem time. > > > > > > > > But doing this on an initcall level was wrong back then, and I have yet to hear > > > > a reason why it would be right this time. > > > > > > It's still wrong, it's not what I was thinking about when talking this > > > over with Luis and Dmitry, I think something got lost in the > > > translation... > > > > Right, all (well almost all) I wanted is for individual drivers to declare > > their probe() functions asynchronous and driver core scheduling async attach > > and properly handle failures from it. > > Yes, that's what I want as well. > > Luis, care to redo the patches in this way? It should be a lot simpler > (no messing around with init levels and linker fun...) Sure, when we spoke the requirement was indeed clear but as I noted on the description on this cover letter as I reviewed Wu Zhangjin's RFC which used async_schedule() he ran into the issue of eventually grouping things. I went with this approach as a first shot given that we have a long tested set of groupings already done by the kernel so this tried to take advantage of that should we try to scale on asynchronous probing. I still believe its a good approach if we wanted to scale it but that would require the desire to do so, I obviously considered it worthwhile as I shaved off at least ~1 second off kernel boot time when doing an original proof of concept and only doing drivers, and taking into consideration my kenrel takes ~5 seconds before userspace is reached. I'll toss this in the bin for now though and send something based on Tejun's approach shortly! Luis