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.
Reviewed-by: Preeti U. Murthy preeti@linux.vnet.ibm.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.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 caeca76d7b32..ee63865d3cd7 100644 --- a/include/linux/clockchips.h +++ b/include/linux/clockchips.h @@ -49,12 +49,15 @@ 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, CLOCK_EVT_STATE_SHUTDOWN, CLOCK_EVT_STATE_PERIODIC, CLOCK_EVT_STATE_ONESHOT, + CLOCK_EVT_STATE_ONESHOT_STOPPED, };
/* @@ -102,6 +105,7 @@ 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 @@ -133,11 +137,12 @@ 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 7af614829da1..49ed2ea4294c 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 e878c2e0ba45..fbc902ccd72a 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);