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SubjectRe: [PATCH 1/3] clocksource: exynos_mct: Fix stall after CPU hotplugging
On 04/15/2014 11:34 AM, Krzysztof Kozlowski wrote:
> On pią, 2014-03-28 at 14:06 +0100, Krzysztof Kozlowski wrote:
>> Fix stall after hotplugging CPU1. Affected are SoCs where Multi Core Timer
>> interrupts are shared (SPI), e.g. Exynos 4210. The stall was a result of
>> starting the CPU1 local timer not in L1 timer but in L0 (which is used
>> by CPU0).
>
> Hi,
>
> Do you have any comments on these 3 patches? They fix the CPU stall on
> Exynos4210 and also on Exynos3250 (Chanwoo Choi sent patches for it
> recently).

You describe this issue as impacting different SoC not only the exynos,
right ?

Do you know what other SoCs are impacted by this ?

I guess this issue is not reproducible just with the line below, we need
a timer to expire right at the moment CPU1 is hotplugged, right ?

>> Trigger:
>> $ echo 0 > /sys/bus/cpu/devices/cpu1/online && echo 1 > /sys/bus/cpu/devices/cpu1/online
>>
>> Stall information:
>> [ 530.045259] INFO: rcu_preempt detected stalls on CPUs/tasks:
>> [ 530.045618] 1: (6 GPs behind) idle=6d0/0/0 softirq=369/369
>> [ 530.050987] (detected by 0, t=6589 jiffies, g=33, c=32, q=0)
>> [ 530.056721] Task dump for CPU 1:
>> [ 530.059928] swapper/1 R running 0 0 1 0x00001000
>> [ 530.066377] [<c0524e14>] (__schedule+0x414/0x9b4) from [<c00b6610>] (rcu_idle_enter+0x18/0x38)
>> [ 530.074955] [<c00b6610>] (rcu_idle_enter+0x18/0x38) from [<c0079a18>] (cpu_startup_entry+0x60/0x3bc)
>> [ 530.084069] [<c0079a18>] (cpu_startup_entry+0x60/0x3bc) from [<c0517d34>] (secondary_start_kernel+0x164/0x1a0)
>> [ 530.094029] [<c0517d34>] (secondary_start_kernel+0x164/0x1a0) from [<40517244>] (0x40517244)
>>
>> The timers for CPU1 were missed:
>> [ 591.668436] cpu: 1
>> [ 591.670430] clock 0:
>> [ 591.672691] .base: c0ab7750
>> [ 591.676160] .index: 0
>> [ 591.679025] .resolution: 1 nsecs
>> [ 591.682404] .get_time: ktime_get
>> [ 591.685970] .offset: 0 nsecs
>> [ 591.689349] active timers:
>> [ 591.692045] #0: <dfb51f40>, hrtimer_wakeup, S:01
>> [ 591.696759] # expires at 454687834257-454687884257 nsecs [in -136770537232 to -136770487232 nsecs]
>>
>> And the event_handler for next event was wrong:
>> [ 591.917120] Tick Device: mode: 1
>> [ 591.920676] Per CPU device: 0
>> [ 591.923621] Clock Event Device: mct_tick0
>> [ 591.927623] max_delta_ns: 178956969027
>> [ 591.931613] min_delta_ns: 1249
>> [ 591.934913] mult: 51539608
>> [ 591.938557] shift: 32
>> [ 591.941681] mode: 3
>> [ 591.944724] next_event: 595025000000 nsecs
>> [ 591.949227] set_next_event: exynos4_tick_set_next_event
>> [ 591.954522] set_mode: exynos4_tick_set_mode
>> [ 591.959296] event_handler: hrtimer_interrupt
>> [ 591.963730] retries: 0
>> [ 591.966761]
>> [ 591.968245] Tick Device: mode: 0
>> [ 591.971801] Per CPU device: 1
>> [ 591.974746] Clock Event Device: mct_tick1
>> [ 591.978750] max_delta_ns: 178956969027
>> [ 591.982739] min_delta_ns: 1249
>> [ 591.986037] mult: 51539608
>> [ 591.989681] shift: 32
>> [ 591.992806] mode: 3
>> [ 591.995848] next_event: 453685000000 nsecs
>> [ 592.000353] set_next_event: exynos4_tick_set_next_event
>> [ 592.005648] set_mode: exynos4_tick_set_mode
>> [ 592.010421] event_handler: tick_handle_periodic
>> [ 592.015115] retries: 0
>> [ 592.018145]
>>
>> After turning off the CPU1, the MCT L1 local timer was disabled but the
>> interrupt was not cleared. Turning on the CPU1 enabled the IRQ
>> with setup_irq() but, before setting affinity to CPU1, the pending L1 timer
>> interrupt was processed by CPU0 in exynos4_mct_tick_isr().
>>
>> The ISR then called event handler which set up the next timer event for
>> current CPU (CPU0). Therefore the MCT L1 timer wasn't actually started.
>>
>> Fix the stall by:
>> 1. Setting next timer event not on current CPU but on the CPU indicated
>> by cpumask in 'clock_event_device'.
>> 2. Clearing the timer interrupt upon stopping the local timer.
>>
>> The patch also moves around the call to exynos4_mct_tick_stop() but this
>> is done only for the code readability as it is not essential for the fix.
>>
>> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
>> Cc: <stable@vger.kernel.org>
>> ---
>> drivers/clocksource/exynos_mct.c | 33 ++++++++++++++++++++-------------
>> 1 file changed, 20 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
>> index 48f76bc05da0..0b49b09dd1a9 100644
>> --- a/drivers/clocksource/exynos_mct.c
>> +++ b/drivers/clocksource/exynos_mct.c
>> @@ -339,7 +339,14 @@ static void exynos4_mct_tick_start(unsigned long cycles,
>> static int exynos4_tick_set_next_event(unsigned long cycles,
>> struct clock_event_device *evt)
>> {
>> - struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
>> + /*
>> + * In case of hotplugging non-boot CPU, the set_next_event could be
>> + * called on CPU0 by ISR before IRQ affinity is set to proper CPU.
>> + * Thus for accessing proper MCT Lx timer, 'per_cpu' for cpumask
>> + * in event must be used instead of 'this_cpu_ptr'.
>> + */
>> + struct mct_clock_event_device *mevt = &per_cpu(percpu_mct_tick,
>> + cpumask_first(evt->cpumask));
>>
>> exynos4_mct_tick_start(cycles, mevt);
>>
>> @@ -371,23 +378,13 @@ static inline void exynos4_tick_set_mode(enum clock_event_mode mode,
>>
>> static int exynos4_mct_tick_clear(struct mct_clock_event_device *mevt)
>> {
>> - struct clock_event_device *evt = &mevt->evt;
>> -
>> - /*
>> - * This is for supporting oneshot mode.
>> - * Mct would generate interrupt periodically
>> - * without explicit stopping.
>> - */
>> - if (evt->mode != CLOCK_EVT_MODE_PERIODIC)
>> - exynos4_mct_tick_stop(mevt);
>> -
>> /* Clear the MCT tick interrupt */
>> if (__raw_readl(reg_base + mevt->base + MCT_L_INT_CSTAT_OFFSET) & 1) {
>> exynos4_mct_write(0x1, mevt->base + MCT_L_INT_CSTAT_OFFSET);
>> return 1;
>> - } else {
>> - return 0;
>> }
>> +
>> + return 0;
>> }
>>
>> static irqreturn_t exynos4_mct_tick_isr(int irq, void *dev_id)
>> @@ -395,6 +392,13 @@ static irqreturn_t exynos4_mct_tick_isr(int irq, void *dev_id)
>> struct mct_clock_event_device *mevt = dev_id;
>> struct clock_event_device *evt = &mevt->evt;
>>
>> + /*
>> + * This is for supporting oneshot mode.
>> + * Mct would generate interrupt periodically
>> + * without explicit stopping.
>> + */
>> + if (evt->mode != CLOCK_EVT_MODE_PERIODIC)
>> + exynos4_mct_tick_stop(mevt);
>> exynos4_mct_tick_clear(mevt);
>>
>> evt->event_handler(evt);
>> @@ -441,7 +445,10 @@ static int exynos4_local_timer_setup(struct clock_event_device *evt)
>>
>> static void exynos4_local_timer_stop(struct clock_event_device *evt)
>> {
>> + struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
>> +
>> evt->set_mode(CLOCK_EVT_MODE_UNUSED, evt);
>> + exynos4_mct_tick_clear(mevt);
>> if (mct_int_type == MCT_INT_SPI)
>> free_irq(evt->irq, this_cpu_ptr(&percpu_mct_tick));
>> else
>


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