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.ku...@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 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 <pre...@linux.vnet.ibm.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/