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Date: Mon, 30 Mar 2015 11:19:30 +0530
From: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To: Viresh Kumar <viresh.kumar@...aro.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>
CC: linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
Kevin Hilman <khilman@...aro.org>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/3] clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED
state
On 03/27/2015 10:44 PM, Viresh Kumar wrote:
> When no timers/hrtimers are pending, the expiry time is set to a special value:
> 'KTIME_MAX'. This normally happens with NO_HZ_{IDLE|FULL} in both LOWRES/HIGHRES
> modes.
>
> When 'expiry == KTIME_MAX', we either cancel the 'tick-sched' hrtimer
> (NOHZ_MODE_HIGHRES) or skip reprogramming clockevent device (NOHZ_MODE_LOWRES).
> But, the clockevent device is already reprogrammed from the tick-handler for
> next tick.
>
> As the clock event device is programmed in ONESHOT mode it will at least fire
> one more time (unnecessarily). Timers on few implementations (like
> arm_arch_timer, etc.) only support PERIODIC mode and their drivers emulate
> ONESHOT over that. Which means that on these platforms we will get spurious
> interrupts periodically (at last programmed interval rate, normally tick rate).
>
> In order to avoid spurious interrupts, the clockevent device should be stopped
> or its interrupts should be masked.
>
> A simple (yet hacky) solution to get this fixed could be: update
> hrtimer_force_reprogram() to always reprogram clockevent device and update
> clockevent drivers to STOP generating events (or delay it to max time) when
> 'expires' is set to KTIME_MAX. But the drawback here is that every clockevent
> driver has to be hacked for this particular case and its very easy for new ones
> to miss this.
>
> However, Thomas suggested to add an optional state ONESHOT_STOPPED to solve this
> problem: lkml.org/lkml/2014/5/9/508.
>
> This patch adds support for ONESHOT_STOPPED state in clockevents core. It will
> only be available to drivers that implement the state-specific callbacks instead
> of the legacy ->set_mode() callback.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> include/linux/clockchips.h | 7 ++++++-
> kernel/time/clockevents.c | 14 +++++++++++++-
> kernel/time/timer_list.c | 6 ++++++
> 3 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
> index e20232c3320a..33ad247f8662 100644
> --- a/include/linux/clockchips.h
> +++ b/include/linux/clockchips.h
> @@ -51,12 +51,15 @@ enum clock_event_mode {
> * reached from DETACHED or SHUTDOWN.
> * ONESHOT: Device is programmed to generate event only once. Can be reached
> * from DETACHED or SHUTDOWN.
> + * ONESHOT_STOPPED: Device was programmed in ONESHOT mode and is temporarily
> + * stopped.
> */
> enum clock_event_state {
> CLOCK_EVT_STATE_DETACHED = 0,
> CLOCK_EVT_STATE_SHUTDOWN,
> CLOCK_EVT_STATE_PERIODIC,
> CLOCK_EVT_STATE_ONESHOT,
> + CLOCK_EVT_STATE_ONESHOT_STOPPED,
> };
>
> /*
> @@ -103,6 +106,7 @@ enum clock_event_state {
> * @set_mode: legacy set mode function, only for modes <= CLOCK_EVT_MODE_RESUME.
> * @set_state_periodic: switch state to periodic, if !set_mode
> * @set_state_oneshot: switch state to oneshot, if !set_mode
> + * @set_state_oneshot_stopped: switch state to oneshot_stopped, if !set_mode
> * @set_state_shutdown: switch state to shutdown, if !set_mode
> * @tick_resume: resume clkevt device, if !set_mode
> * @broadcast: function to broadcast events
> @@ -136,12 +140,13 @@ struct clock_event_device {
> * State transition callback(s): Only one of the two groups should be
> * defined:
> * - set_mode(), only for modes <= CLOCK_EVT_MODE_RESUME.
> - * - set_state_{shutdown|periodic|oneshot}(), tick_resume().
> + * - set_state_{shutdown|periodic|oneshot|oneshot_stopped}(), tick_resume().
> */
> void (*set_mode)(enum clock_event_mode mode,
> struct clock_event_device *);
> int (*set_state_periodic)(struct clock_event_device *);
> int (*set_state_oneshot)(struct clock_event_device *);
> + int (*set_state_oneshot_stopped)(struct clock_event_device *);
> int (*set_state_shutdown)(struct clock_event_device *);
> int (*tick_resume)(struct clock_event_device *);
>
> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
> index 73689df1e4b8..04f6c3433f8e 100644
> --- a/kernel/time/clockevents.c
> +++ b/kernel/time/clockevents.c
> @@ -138,6 +138,17 @@ static int __clockevents_set_state(struct clock_event_device *dev,
> return -ENOSYS;
> return dev->set_state_oneshot(dev);
>
> + case CLOCK_EVT_STATE_ONESHOT_STOPPED:
> + /* Core internal bug */
> + if (WARN_ONCE(dev->state != CLOCK_EVT_STATE_ONESHOT,
> + "Current state: %d\n", dev->state))
> + return -EINVAL;
> +
> + if (dev->set_state_oneshot_stopped)
> + return dev->set_state_oneshot_stopped(dev);
> + else
> + return -ENOSYS;
> +
> default:
> return -ENOSYS;
> }
> @@ -449,7 +460,8 @@ static int clockevents_sanity_check(struct clock_event_device *dev)
> if (dev->set_mode) {
> /* We shouldn't be supporting new modes now */
> WARN_ON(dev->set_state_periodic || dev->set_state_oneshot ||
> - dev->set_state_shutdown || dev->tick_resume);
> + dev->set_state_shutdown || dev->tick_resume ||
> + dev->set_state_oneshot_stopped);
>
> BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
> return 0;
> diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
> index 05aa5590106a..98d77969ba85 100644
> --- a/kernel/time/timer_list.c
> +++ b/kernel/time/timer_list.c
> @@ -251,6 +251,12 @@ print_tickdevice(struct seq_file *m, struct tick_device *td, int cpu)
> SEQ_printf(m, "\n");
> }
>
> + if (dev->set_state_oneshot_stopped) {
> + SEQ_printf(m, " oneshot stopped: ");
> + print_name_offset(m, dev->set_state_oneshot_stopped);
> + SEQ_printf(m, "\n");
> + }
> +
> if (dev->tick_resume) {
> SEQ_printf(m, " resume: ");
> print_name_offset(m, dev->tick_resume);
>
With all the precursor patches gone in, this series looks good to me.
Reviewed-by: Preeti U. Murthy <preeti@...ux.vnet.ibm.com>
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