From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755325AbbAZNnK (ORCPT ); Mon, 26 Jan 2015 08:43:10 -0500 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:53898 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753480AbbAZNnH (ORCPT ); Mon, 26 Jan 2015 08:43:07 -0500 Date: Mon, 26 Jan 2015 14:43:04 +0100 From: Pavel Machek To: "Rafael J. Wysocki" Cc: "Liu, Chuansheng" , "Fu, Zhonghui" , "Brown, Len" , Greg Kroah-Hartman , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , trivial@kernel.org Subject: Re: Change behaviour when tracing ... nasty trap (was Re: [PATCH] PM/Trace: get rid of synchronous resume limit during PM trace) Message-ID: <20150126134304.GA7889@amd> References: <54C5CB77.4000109@linux.intel.com> <27240C0AC20F114CBF8149A2696CBE4A01F1AD6A@SHSMSX101.ccr.corp.intel.com> <20150126110516.GA2028@amd> <2718950.eck1siDzqK@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2718950.eck1siDzqK@vostro.rjw.lan> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Document pm_tracing actually affecting suspend in non-trivial way. Signed-off-by: Pavel Machek --- On Mon 2015-01-26 14:41:02, Rafael J. Wysocki wrote: > On Monday, January 26, 2015 12:05:16 PM Pavel Machek wrote: > > On Mon 2015-01-26 10:39:04, Liu, Chuansheng wrote: > > > > > @@ -517,8 +517,7 @@ static int device_resume_noirq(struct device *dev, > > > > pm_message_t state, bool asyn > > > > > > > > > > static bool is_async(struct device *dev) > > > > > { > > > > > - return dev->power.async_suspend && pm_async_enabled > > > > > - && !pm_trace_is_enabled(); > > > > > + return dev->power.async_suspend && pm_async_enabled; > > > > > } > > > > > > > > > > > > > Actually... whoever did the original patch was evil person. Changing > > > > behaviour when tracing is requested is evil, evil, evil. Git blame > > > > tells me > > > > > > > > Signed-off-by: Chuansheng Liu > > > > > > > > went to the dark side. > > > > > > Although I didn't get where is something wrong, but the is_async() is not created by my commit, > > > it is from commit (PM: Start asynchronous resume threads upfront), I just moved it ahead. > > > > > > And like other phases, I added it into resum/suspend_noirq()... > > > > I see, blame blamed wrong person. It looks like Rafael is evil: > > > > commit 97df8c12995c5bac73e3bfeea4c5be155c1f4401 > > Author: Rafael J. Wysocki > > Date: Sat Jan 23 22:25:31 2010 +0100 > > > > PM: Start asynchronous resume threads upfront > > This only means we won't use asyc suspend/resume at all when the RTC-based > resume debug is enabled, because it wouldn't make sense (the RTC-based > debug requires strict ordering of callbacks between devices or we may find > that device A hanged the resume while actually device B that was running in > parallel with A did that). > > And I shouldn't even need to explain this ... Sad. Well, I forgot that pm_trace_is_enabled() is the simple, RTC based one, and believe it would be worth a comment... diff --git a/Documentation/power/s2ram.txt b/Documentation/power/s2ram.txt index 1bdfa04..4685aee 100644 --- a/Documentation/power/s2ram.txt +++ b/Documentation/power/s2ram.txt @@ -69,6 +69,10 @@ Reason for this is that the RTC is the only reliably available piece of hardware during resume operations where a value can be set that will survive a reboot. +pm_trace is not compatible with asynchronous suspend, so it turns +asynchronous suspend off (which may work around timing or +ordering-sensitive bugs). + Consequence is that after a resume (even if it is successful) your system clock will have a value corresponding to the magic number instead of the correct date/time! It is therefore advisable to use a program like ntp-date -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html