Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754948Ab3HFIqz (ORCPT ); Tue, 6 Aug 2013 04:46:55 -0400 Received: from mail-wg0-f50.google.com ([74.125.82.50]:46127 "EHLO mail-wg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754661Ab3HFIqu (ORCPT ); Tue, 6 Aug 2013 04:46:50 -0400 Message-ID: <5200B7FE.4000306@linaro.org> Date: Tue, 06 Aug 2013 10:46:54 +0200 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: =?UTF-8?B?U8O2cmVuIEJyaW5rbWFubg==?= CC: Stuart Menefy , Stephen Boyd , John Stultz , Thomas Gleixner , Russell King , Michal Simek , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: Enable arm_global_timer for Zynq brakes boot References: <51F77D93.4030505@linaro.org> <51F97842.6050200@linaro.org> <068436c6-ff98-428f-8875-bb1c6f86466b@TX2EHSMHS008.ehs.local> <51F97CE3.9030306@linaro.org> <15e19315-ce88-4d3c-bad9-0a37d9e52f6b@CO1EHSMHS007.ehs.local> <51F99747.4060901@linaro.org> <51FA9AE8.1060004@linaro.org> <1c83c081-60c6-49e3-a85c-f64dd5be0e60@CH1EHSMHS030.ehs.local> <51FA9F54.3060704@linaro.org> <712d31e9-3584-48e1-aa9f-55bc94fa62c9@DB9EHSMHS001.ehs.local> In-Reply-To: <712d31e9-3584-48e1-aa9f-55bc94fa62c9@DB9EHSMHS001.ehs.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8232 Lines: 175 On 08/06/2013 03:28 AM, Sören Brinkmann wrote: > Hi Daniel, > > On Thu, Aug 01, 2013 at 07:48:04PM +0200, Daniel Lezcano wrote: >> On 08/01/2013 07:43 PM, Sören Brinkmann wrote: >>> On Thu, Aug 01, 2013 at 07:29:12PM +0200, Daniel Lezcano wrote: >>>> On 08/01/2013 01:38 AM, Sören Brinkmann wrote: >>>>> On Thu, Aug 01, 2013 at 01:01:27AM +0200, Daniel Lezcano wrote: >>>>>> On 08/01/2013 12:18 AM, Sören Brinkmann wrote: >>>>>>> On Wed, Jul 31, 2013 at 11:08:51PM +0200, Daniel Lezcano wrote: >>>>>>>> On 07/31/2013 10:58 PM, Sören Brinkmann wrote: >>>>>>>>> On Wed, Jul 31, 2013 at 10:49:06PM +0200, Daniel Lezcano wrote: >>>>>>>>>> On 07/31/2013 12:34 AM, Sören Brinkmann wrote: >>>>>>>>>>> On Tue, Jul 30, 2013 at 10:47:15AM +0200, Daniel Lezcano wrote: >>>>>>>>>>>> On 07/30/2013 02:03 AM, Sören Brinkmann wrote: >>>>>>>>>>>>> Hi Daniel, >>>>>>>>>>>>> >>>>>>>>>>>>> On Mon, Jul 29, 2013 at 02:51:49PM +0200, Daniel Lezcano wrote: >>>>>>>>>>>>> (snip) >>>>>>>>>>>>>> >>>>>>>>>>>>>> the CPUIDLE_FLAG_TIMER_STOP flag tells the cpuidle framework the local >>>>>>>>>>>>>> timer will be stopped when entering to the idle state. In this case, the >>>>>>>>>>>>>> cpuidle framework will call clockevents_notify(ENTER) and switches to a >>>>>>>>>>>>>> broadcast timer and will call clockevents_notify(EXIT) when exiting the >>>>>>>>>>>>>> idle state, switching the local timer back in use. >>>>>>>>>>>>> >>>>>>>>>>>>> I've been thinking about this, trying to understand how this makes my >>>>>>>>>>>>> boot attempts on Zynq hang. IIUC, the wrongly provided TIMER_STOP flag >>>>>>>>>>>>> would make the timer core switch to a broadcast device even though it >>>>>>>>>>>>> wouldn't be necessary. But shouldn't it still work? It sounds like we do >>>>>>>>>>>>> something useless, but nothing wrong in a sense that it should result in >>>>>>>>>>>>> breakage. I guess I'm missing something obvious. This timer system will >>>>>>>>>>>>> always remain a mystery to me. >>>>>>>>>>>>> >>>>>>>>>>>>> Actually this more or less leads to the question: What is this >>>>>>>>>>>>> 'broadcast timer'. I guess that is some clockevent device which is >>>>>>>>>>>>> common to all cores? (that would be the cadence_ttc for Zynq). Is the >>>>>>>>>>>>> hang pointing to some issue with that driver? >>>>>>>>>>>> >>>>>>>>>>>> If you look at the /proc/timer_list, which timer is used for broadcasting ? >>>>>>>>>>> >>>>>>>>>>> So, the correct run results (full output attached). >>>>>>>>>>> >>>>>>>>>>> The vanilla kernel uses the twd timers as local timers and the TTC as >>>>>>>>>>> broadcast device: >>>>>>>>>>> Tick Device: mode: 1 >>>>>>>>>>> Broadcast device >>>>>>>>>>> Clock Event Device: ttc_clockevent >>>>>>>>>>> >>>>>>>>>>> When I remove the offending CPUIDLE flag and add the DT fragment to >>>>>>>>>>> enable the global timer, the twd timers are still used as local timers >>>>>>>>>>> and the broadcast device is the global timer: >>>>>>>>>>> Tick Device: mode: 1 >>>>>>>>>>> Broadcast device >>>>>>>>>>> Clock Event Device: arm_global_timer >>>>>>>>>>> >>>>>>>>>>> Again, since boot hangs in the actually broken case, I don't see way to >>>>>>>>>>> obtain this information for that case. >>>>>>>>>> >>>>>>>>>> Can't you use the maxcpus=1 option to ensure the system to boot up ? >>>>>>>>> >>>>>>>>> Right, that works. I forgot about that option after you mentioned, that >>>>>>>>> it is most likely not that useful. >>>>>>>>> >>>>>>>>> Anyway, this are those sysfs files with an unmodified cpuidle driver and >>>>>>>>> the gt enabled and having maxcpus=1 set. >>>>>>>>> >>>>>>>>> /proc/timer_list: >>>>>>>>> Tick Device: mode: 1 >>>>>>>>> Broadcast device >>>>>>>>> Clock Event Device: arm_global_timer >>>>>>>>> max_delta_ns: 12884902005 >>>>>>>>> min_delta_ns: 1000 >>>>>>>>> mult: 715827876 >>>>>>>>> shift: 31 >>>>>>>>> mode: 3 >>>>>>>> >>>>>>>> Here the mode is 3 (CLOCK_EVT_MODE_ONESHOT) >>>>>>>> >>>>>>>> The previous timer_list output you gave me when removing the offending >>>>>>>> cpuidle flag, it was 1 (CLOCK_EVT_MODE_SHUTDOWN). >>>>>>>> >>>>>>>> Is it possible you try to get this output again right after onlining the >>>>>>>> cpu1 in order to check if the broadcast device switches to SHUTDOWN ? >>>>>>> >>>>>>> How do I do that? I tried to online CPU1 after booting with maxcpus=1 >>>>>>> and that didn't end well: >>>>>>> # echo 1 > online && cat /proc/timer_list >>>>>> >>>>>> Hmm, I was hoping to have a small delay before the kernel hangs but >>>>>> apparently this is not the case... :( >>>>>> >>>>>> I suspect the global timer is shutdown at one moment but I don't >>>>>> understand why and when. >>>>>> >>>>>> Can you add a stack trace in the "clockevents_shutdown" function with >>>>>> the clockevent device name ? Perhaps, we may see at boot time an >>>>>> interesting trace when it hangs. >>>>> >>>>> I did this change: >>>>> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c >>>>> index 38959c8..3ab11c1 100644 >>>>> --- a/kernel/time/clockevents.c >>>>> +++ b/kernel/time/clockevents.c >>>>> @@ -92,6 +92,8 @@ void clockevents_set_mode(struct clock_event_device *dev, >>>>> */ >>>>> void clockevents_shutdown(struct clock_event_device *dev) >>>>> { >>>>> + pr_info("ce->name:%s\n", dev->name); >>>>> + dump_stack(); >>>>> clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN); >>>>> dev->next_event.tv64 = KTIME_MAX; >>>>> } >>>>> >>>>> It is hit a few times during boot, so I attach a full boot log. I really >>>>> don't know what to look for, but I hope you can spot something in it. I >>>>> really appreciate you taking the time. >>>> >>>> Thanks for the traces. >>> >>> Sure. >>> >>>> >>>> If you try without the ttc_clockevent configured in the kernel (but with >>>> twd and gt), does it boot ? >>> >>> Absence of the TTC doesn't seem to make any difference. It hangs at the >>> same location. >> >> Ok, IMO there is a problem with the broadcast device registration (may >> be vs twd). >> >> I will check later (kid duty) :) > > I was actually waiting for an update from your side and did something > else, but I seem to have run into this again. I was overhauling the > cadence_ttc (patch attached, based on tip/timers/core). And it seems to > show the same behavior as enabling the global_timer. With cpuidle off, it > works. With cpuidle, on it hangs. Removing the TIMER_STOP flag from the > C2 state makes it boot again. > It works just fine on our 3.10 kernel. This is not necessary related to the bug. If the patch you sent broke the cadence_ttc driver, when you use it (with the TIMER_STOP), you will be stuck. Removing the flag, may signifies you don't use the broadcast timer, hence the bug is not surfacing. Going back to the bug with the arm_global_timer, what is observed is the broadcast timer is *shutdown* when the second cpu is online. I have to dig into the kernel/time/clockevents.c|tick-*.c because IMO the issue is coming from there but before I have to reproduce the bug, so find a board I have where I can add the arm_global_timer. > Another thing I noticed - probably unrelated but hard to tell: On > 3.11-rc1 and later my system stops for quite some time at the hand off > to userspace. I.e. I see the 'freeing unused kernel memory...' line and > sometimes the following 'Welcome to Buildroot...' and then it stops and > on good kernels it continues after a while and boots through and on bad > ones it just hangs there. did you try to dump the stacks with magic-sysrq ? 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