By default, the watchdog threshold is 10, it means every 4s every CPU will receive one hrtimer interrupt, for low power device, it will cause 4-5mV power impact when device is deep sleep.
So here want to optimize it as below: 4s + 4s + 4s + 4s + 4s == > 12s + 2s + 2s + 2s + 2s 3/5 1/10 1/10 1/10 1/10 In 5 chances, once one chance is hit, then we can start the hrtimer with a longer period sample(12s). Until the current chance is not hit, will start the hrtimer with a shorted period sample(2s). With this patch, in most case the hrtimer will be 12s instead of 4s averagely. It can save the device power indeed. Signed-off-by: liu chuansheng <[email protected]> --- kernel/watchdog.c | 30 ++++++++++++++++++++++++++++-- 1 files changed, 28 insertions(+), 2 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index dd4b80a..6457e62 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -125,7 +125,24 @@ static u64 get_sample_period(void) * and hard thresholds) to increment before the * hardlockup detector generates a warning */ - return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5); + return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 10); +} + +static u64 get_long_sample_period(void) +{ + /* + * convert watchdog_thresh from seconds to ns + * We want to give 5 chances to detect softlockup, + * for power saving, once one chance is succeeding, + * we can set long period to avoid power consumption. + * Currently, set the long sample period is: + * 20s * 3/5 = 12s, once this 12s chance is not hit, + * we will divide the left 8s into 4 pieces, give every + * chance every 2s, so it will be likely: + * 12s + 2s + 2s + 2s + 2s, + * Anyway, we just use 12s is enough in normal case. + */ + return get_softlockup_thresh() * ((u64)NSEC_PER_SEC * 3 / 5); } /* Commands for resetting the watchdog */ @@ -267,6 +284,10 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts); struct pt_regs *regs = get_irq_regs(); int duration; + bool is_touched; + + is_touched = (__this_cpu_read(hrtimer_interrupts) == + __this_cpu_read(soft_lockup_hrtimer_cnt)); /* kick the hardlockup detector */ watchdog_interrupt_count(); @@ -275,7 +296,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) wake_up_process(__this_cpu_read(softlockup_watchdog)); /* .. and repeat */ - hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period())); + if (is_touched) { + hrtimer_forward_now(hrtimer, + ns_to_ktime(get_long_sample_period())); + } else { + hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period())); + } if (touch_ts == 0) { if (unlikely(__this_cpu_read(softlockup_touch_sync))) { -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
