Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965900Ab3HHRRb (ORCPT ); Thu, 8 Aug 2013 13:17:31 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:35468 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965361Ab3HHRRa (ORCPT ); Thu, 8 Aug 2013 13:17:30 -0400 Date: Thu, 8 Aug 2013 18:16:50 +0100 From: Mark Rutland To: =?utf-8?B?U8O2cmVu?= Brinkmann Cc: Daniel Lezcano , Russell King , Stephen Boyd , Michal Simek , "linux-kernel@vger.kernel.org" , Stuart Menefy , John Stultz , Thomas Gleixner , "linux-arm-kernel@lists.infradead.org" Subject: Re: Enable arm_global_timer for Zynq brakes boot Message-ID: <20130808171650.GH27325@e106331-lin.cambridge.arm.com> References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7787 Lines: 166 On Thu, Aug 08, 2013 at 06:11:26PM +0100, 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 have an idea, but no real evidence to prove it: > Some of the registers in the arm_global_timer are banked per CPU. I.e. > some code must be executed on the CPU the timer is associated with > (struct clock_event_device.cpumask) to have the intended effect > As far as I can tell, there is no guarantee, that the set_mode() > and program_next_event() calls execute on the correct CPU. I believe the core clockevents code enforces that, or all other percpu clockevent_device drivers would be horrifically broken. Thanks, Mark. > If this was correct, shutting down the timer for the CPU entering > idle might actually shut down the timer for the running CPU, if > set_mode() executes on the CPU which is _not_ about to enter idle. > > I tried to prove this by adding some really ugly smp_call_any() wrappers > in kernel/time/clockevents.c for the calls to set_mode() and > program_net_event() but that ends in all kinds of dead locks. > > Sören > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- 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/