From mboxrd@z Thu Jan 1 00:00:00 1970 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 From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lorenzo Pieralisi Subject: Re: [PATCH RFC v1 3/3] ARM hibernation / suspend-to-disk Date: Tue, 25 Feb 2014 11:32:51 +0000 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 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: 8BIT Return-path: Received: from service87.mimecast.com ([91.220.42.44]:59474 "EHLO service87.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752118AbaBYLc4 convert rfc822-to-8bit (ORCPT ); Tue, 25 Feb 2014 06:32:56 -0500 In-Reply-To: <20140223200208.12998.47604@capellas-linux> Content-Disposition: inline Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org 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" 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 From mboxrd@z Thu Jan 1 00:00:00 1970 From: lorenzo.pieralisi@arm.com (Lorenzo Pieralisi) Date: Tue, 25 Feb 2014 11:32:51 +0000 Subject: [PATCH RFC v1 3/3] ARM hibernation / suspend-to-disk In-Reply-To: <20140223200208.12998.47604@capellas-linux> 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> Message-ID: <20140225113251.GB6855@e102568-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.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