Messages in this thread | | | Date | Wed, 31 Jul 2013 15:18:00 -0700 | From | Sören Brinkmann <> | Subject | Re: Enable arm_global_timer for Zynq brakes boot |
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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 [ 4689.992658] CPU1: Booted secondary processor [ 4690.986295] CPU1: failed to come online sh: write error: Input/output error # [ 4691.045945] CPU1: thread -1, cpu 1, socket 0, mpidr 80000001 [ 4691.045986] [ 4691.052972] =============================== [ 4691.057349] [ INFO: suspicious RCU usage. ] [ 4691.061413] 3.11.0-rc3-00001-gc14f576-dirty #139 Not tainted [ 4691.067026] ------------------------------- [ 4691.071129] kernel/sched/fair.c:5477 suspicious rcu_dereference_check() usage! [ 4691.078292] [ 4691.078292] other info that might help us debug this: [ 4691.078292] [ 4691.086209] [ 4691.086209] RCU used illegally from offline CPU! [ 4691.086209] rcu_scheduler_active = 1, debug_locks = 0 [ 4691.097216] 1 lock held by swapper/1/0: [ 4691.100968] #0: (rcu_read_lock){.+.+..}, at: [<c00679b4>] set_cpu_sd_state_idle+0x0/0x1e4 [ 4691.109250] [ 4691.109250] stack backtrace: [ 4691.113531] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.11.0-rc3-00001-gc14f576-dirty #139 [ 4691.121755] [<c0016a88>] (unwind_backtrace+0x0/0x128) from [<c0012d58>] (show_stack+0x20/0x24) [ 4691.130263] [<c0012d58>] (show_stack+0x20/0x24) from [<c045bd50>] (dump_stack+0x80/0xc4) [ 4691.138264] [<c045bd50>] (dump_stack+0x80/0xc4) from [<c007ad78>] (lockdep_rcu_suspicious+0xdc/0x118) [ 4691.147371] [<c007ad78>] (lockdep_rcu_suspicious+0xdc/0x118) from [<c0067ac0>] (set_cpu_sd_state_idle+0x10c/0x1e4) [ 4691.157605] [<c0067ac0>] (set_cpu_sd_state_idle+0x10c/0x1e4) from [<c0078238>] (tick_nohz_idle_enter+0x48/0x80) [ 4691.167583] [<c0078238>] (tick_nohz_idle_enter+0x48/0x80) from [<c006dc5c>] (cpu_startup_entry+0x28/0x388) [ 4691.177127] [<c006dc5c>] (cpu_startup_entry+0x28/0x388) from [<c0014acc>] (secondary_start_kernel+0x12c/0x144) [ 4691.187013] [<c0014acc>] (secondary_start_kernel+0x12c/0x144) from [<000081ec>] (0x81ec)
Sören
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