Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966751AbZLHWco (ORCPT ); Tue, 8 Dec 2009 17:32:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S966530AbZLHWcj (ORCPT ); Tue, 8 Dec 2009 17:32:39 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:39280 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966378AbZLHWcj (ORCPT ); Tue, 8 Dec 2009 17:32:39 -0500 Date: Tue, 8 Dec 2009 14:32:40 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Alan Stern cc: "Rafael J. Wysocki" , Zhang Rui , LKML , ACPI Devel Maling List , pm list Subject: Re: Async resume patch (was: Re: [GIT PULL] PM updates for 2.6.33) In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1968 Lines: 56 On Tue, 8 Dec 2009, Alan Stern wrote: > > Suppose A and B are unrelated devices and we need to impose the > off-tree constraint that A suspends after B. Ah. Ok, I can imagine the off-tree constraints, but part of my "keep it simple" was to simply not do them. If there are constraints that aren't in the topology of the tree, then I simply don't think that async is worth it in the first place. > You misunderstand. The suspend algorithm will look like this: > > dpm_suspend() > { > list_for_each_entry_reverse(dpm_list, dev) { > down_write(dev->lock); > async_schedule(device_suspend, dev); > } > } > > device_suspend(dev) > { > device_for_each_child(dev, child) { > down_read(child->lock); > up_read(child->lock); > } > dev->suspend(dev); /* May do off-tree down+up pairs */ > up_write(dev->lock); > } Ok, so the above I think work (and see my previous email: I think completions would be workable there too). It's just that I think the "looping over children" is ugly, when I think that by doing it the other way around you can make the code simpler and only depend on the PM device list and a simple parent pointer access. I also think that you are wrong that the above somehow protects against non-topological dependencies. If the device you want to keep delay yourself suspending for is after you in the list, the down_read() on that may succeed simply because it hasn't even done its down_write() yet and you got scheduled early. But I guess you could do that by walking the list twice (first to lock them all, then to actually call the suspend function). That whole two-phase thing, except the first phase _only_ locks, and doesn't do any callbacks. Linus -- 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/