Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753122AbaBYLc6 (ORCPT ); Tue, 25 Feb 2014 06:32:58 -0500 Received: from service87.mimecast.com ([91.220.42.44]:59471 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751344AbaBYLc4 convert rfc822-to-8bit (ORCPT ); Tue, 25 Feb 2014 06:32:56 -0500 Date: Tue, 25 Feb 2014 11:32:51 +0000 From: Lorenzo Pieralisi To: Sebastian Capella Cc: Russell King - ARM Linux , Len Brown , "linaro-kernel@lists.linaro.org" , Catalin Marinas , Jonathan Austin , "linux-pm@vger.kernel.org" , Will Deacon , Nicolas Pitre , "Rafael J. Wysocki" , "linux-kernel@vger.kernel.org" , Uwe Kleine-K?nig , Russ Dill , Pavel Machek , Cyril Chemparathy , Santosh Shilimkar , Stephen Boyd , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH RFC v1 3/3] ARM hibernation / suspend-to-disk Message-ID: <20140225113251.GB6855@e102568-lin.cambridge.arm.com> References: <1392774729-3235-1-git-send-email-sebastian.capella@linaro.org> <1392774729-3235-4-git-send-email-sebastian.capella@linaro.org> <20140219161254.GB19343@e102568-lin.cambridge.arm.com> <20140222103840.GH21483@n2100.arm.linux.org.uk> <20140222120910.GA9012@e102568-lin.cambridge.arm.com> <20140223200208.12998.47604@capellas-linux> MIME-Version: 1.0 In-Reply-To: <20140223200208.12998.47604@capellas-linux> User-Agent: Mutt/1.5.21 (2010-09-15) X-OriginalArrivalTime: 25 Feb 2014 11:32:58.0262 (UTC) FILETIME=[553E4B60:01CF321D] X-MC-Unique: 114022511325305701 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Feb 23, 2014 at 08:02:08PM +0000, Sebastian Capella wrote: > Quoting Lorenzo Pieralisi (2014-02-22 04:09:10) > > On Sat, Feb 22, 2014 at 10:38:40AM +0000, Russell King - ARM Linux wrote: > > > On Wed, Feb 19, 2014 at 04:12:54PM +0000, Lorenzo Pieralisi wrote: > > > > On Wed, Feb 19, 2014 at 01:52:09AM +0000, Sebastian Capella wrote: > > > > > +/* > > > > > + * Snapshot kernel memory and reset the system. > > > > > + * After resume, the hibernation snapshot is written out. > > > > > + */ > > > > > +static int notrace __swsusp_arch_save_image(unsigned long unused) > > > > > +{ > > > > > + int ret; > > > > > + > > > > > + ret = swsusp_save(); > > > > > + if (ret == 0) > > > > > + soft_restart(virt_to_phys(cpu_resume)); > > > > > > > > By the time the suspend finisher (ie this function) is run, the > > > > processor state has been saved and I think that's all you have to do, > > > > function can just return after calling swsusp_save(), unless I am missing > > > > something. > > > > > > > > I do not understand why a soft_restart is required here. On a side note, > > > > finisher is called with irqs disabled so, since you added a function for > > > > soft restart noirq, it should be used, if needed, but I have to understand > > > > why in the first place. > > > > > > It's required because you can't just return from the finisher. A normal > > > return from the finisher will always be interpreted as an abort rather > > > than success (because the state has to be unwound.) > > > > > > This is the only way to get a zero return from cpu_suspend(). > > > > Yes, that's the only reason why this code is jumping to cpu_resume, since > > all it is needed is to snapshot the CPU context and by the time the > > finisher is called that's done. Wanted to say that soft reboot is not > > useful (cache flushing and resume with MMU off), but what you are saying > > is correct. We might be saving swsusp_save return value in a global > > variable and just return from the finisher, but that's horrible and > > given the amount of time it takes to snapshot the image to disk the > > cost of this soft reboot will be dwarfed by that. > > > > I wanted to ask and clarify why the code was written like this though, given > > its complexity. > > We could also return a constant > 1. __cpu_suspend code will replace > a 0 return with 1 for paths exiting suspend, but will not change return > values != 0. Yes, we could but that's an API abuse and as I mentioned that soft_reboot is not a massive deal, should not block your series. It is certainly something to be benchmarked though since wiping the entire cache hierarchy for nothing is not nifty. > cpu_suspend_abort: > ldmia sp!, {r1 - r3} @ pop phys pgd, virt SP, phys > resume fn > teq r0, #0 > moveq r0, #1 @ force non-zero value > mov sp, r2 > ldmfd sp!, {r4 - r11, pc} > > We could take advantage of that if we wanted, but Lorenzo pointed out > also that the relative benefit is very low since the cost of > resuming is >> soft_restart. The cost of writing to disk, to be precise. Again, this should be benchmarked. > I'll go with leaving the soft_restart as is unless someone feels > strongly against. Leaving it as it is is fine for now, but should be commented, because that's not clear why it is needed by just reading the code. Thanks, Lorenzo -- 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/