linux-kernel - Re: [PATCH] x86/apic: Implement set_state_oneshot

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Date:   Fri, 30 Dec 2016 09:28:53 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Frederic Weisbecker <fweisbec@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Ingo Molnar <mingo@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH] x86/apic: Implement set_state_oneshot_stopped() callback

2016-12-30 0:45 GMT+08:00 Frederic Weisbecker <fweisbec@...il.com>:
> When clock_event_device::set_state_oneshot_stopped() is not implemented,
> hrtimer_cancel() can't stop the clock when there is no more timer in
> the queue. So the ghost of the freshly cancelled hrtimer haunts us back
> later with an extra interrupt:
>
>           <idle>-0     [002] d..2  2248.557659: hrtimer_cancel: hrtimer=ffff88021fa92d80
>           <idle>-0     [002] d.h1  2249.303659: local_timer_entry: vector=239
>
> So let's implement this missing callback for the lapic clock. This
> consist in calling its set_state_shutdown() callback. There don't seem
> to be a lighter way to stop the clock. Simply writing 0 to APIC_TMICT
> won't be enough to stop the clock and avoid the extra interrupt, as
> opposed to what is specified in the specs. We must also mask the
> timer interrupt in the device.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Wanpeng Li <wanpeng.li@...mail.com>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---

Reviewed-by: Wanpeng Li <wanpeng.li@...mail.com>

>  arch/x86/kernel/apic/apic.c | 25 +++++++++++++------------
>  1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 5b7e43e..a8e90db 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -529,18 +529,19 @@ static void lapic_timer_broadcast(const struct cpumask *mask)
>   * The local apic timer can be used for any function which is CPU local.
>   */
>  static struct clock_event_device lapic_clockevent = {
> -       .name                   = "lapic",
> -       .features               = CLOCK_EVT_FEAT_PERIODIC |
> -                                 CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP
> -                                 | CLOCK_EVT_FEAT_DUMMY,
> -       .shift                  = 32,
> -       .set_state_shutdown     = lapic_timer_shutdown,
> -       .set_state_periodic     = lapic_timer_set_periodic,
> -       .set_state_oneshot      = lapic_timer_set_oneshot,
> -       .set_next_event         = lapic_next_event,
> -       .broadcast              = lapic_timer_broadcast,
> -       .rating                 = 100,
> -       .irq                    = -1,
> +       .name                           = "lapic",
> +       .features                       = CLOCK_EVT_FEAT_PERIODIC |
> +                                         CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP
> +                                         | CLOCK_EVT_FEAT_DUMMY,
> +       .shift                          = 32,
> +       .set_state_shutdown             = lapic_timer_shutdown,
> +       .set_state_periodic             = lapic_timer_set_periodic,
> +       .set_state_oneshot              = lapic_timer_set_oneshot,
> +       .set_state_oneshot_stopped      = lapic_timer_shutdown,
> +       .set_next_event                 = lapic_next_event,
> +       .broadcast                      = lapic_timer_broadcast,
> +       .rating                         = 100,
> +       .irq                            = -1,
>  };
>  static DEFINE_PER_CPU(struct clock_event_device, lapic_events);
>
> --
> 2.7.4
>